[Desert Rodent]

Are you are getting a P0420 code?? If not, what code are you getting with the check engine light??
If you had a problem with the exhaust flange, I'd think you would see a hole in the exhaust pipe where the flange is welded on. There is a gasket between the two flanges, but I don't see that going bad. Did something impact the exhaust system (run over something)?? Is the vehicle LOUD?? (especially when you accelerate)
Unless you have A LOT of miles on the car, I can't see a catalytic converter going bad on a 2017 (unless it was exposed to extra unburned gas like a misfire for a long time). Did you have any "check engine" light codes prior to this P0420 code??

 

[Desert Rodent]

yes I was riding with misfire for a while long time

With a misfire code, you are sending unburned gasoline into the catalytic converter and it begins to get polluted and damaged. If you fix the misfire quickly, then no harm is done to the catalytic converter, whereas if you drive for extended periods of time with a misfire the catalytic converter will become damaged and eventually fail. At that point, you get a P0420 code.
Let me qualify that I'm just a "shade tree" mechanic, but in my experience EVERY P0420 code is a bad catalytic converter.
For testing purposes, I've used a homemade device called a "Spark Plug Anti-fouler trick" on the downstream Oxygen Sensor. This "spark plug anti-fouler trick" may or may not be legal in your state. You may want to google some information on it, as well as look at some of the youtube videos. I'm sure there is a better way to test to see if your catalytic converter is bad, but I don't have any of that equipment.
Personally, I've had good luck with ebay catalytic converters on my previous GM vehicles, I have not had to put a cat on a Nissan product, yet. You may also want to look at rockauto and price a new catalytic converter.

...and you might be right if somebody else took my car for Joy ride hit something underneath car might be a leak somewhere...

If the exhaust were leaking somewhere in the system, it should be fairly loud and fairly obvious. That is not to say that a visual inspection should be ruled out. If it were my car, I would do a good visual inspection of the exhaust system. And if you are going to get underneath the car, please use a good quality jack stand to support the car.

 

[Desert Rodent]

With the OBD2 monitoring system, the car runs monitors on the emissions equipment and other systems. When you delete the P0420 code with your code reader (or disconnect the battery), the car thinks you have completed a repair, so it resets all of the monitors to zero and starts to perform a self diagnosis on its systems. To get all of the monitors reset, the car puts itself through a "drive cycle". As you drive, it begins to check things off on the "drive cycle", if while performing this drive cycle the car encounters a problem or anomaly it turns on the "check engine light".
So each time you delete the P0420 code, the catalyst monitor goes back to zero and starts to perform a self diagnosis, because you haven't fixed the catalytic converter, the computer doesn't like the values it sees coming from the 02 sensor and throws the P0420 code.
You may want to familiarize yourself with the Nissan "drive cycle". It checks the EVAP system, catalyst, 02 sensors, EGR, etc.
Do you have take the car through an emissions inspection??

 

[Desert Rodent]

The Evap system is different from the catalyst system, thus there are different codes for an EVAP leak or problem with the EVAP system. (Gasoline evaporating)
The catalyst system has to do with exhaust gases. The catalytic converter attempts to clean up the exhaust gases coming from the engine before they exit the tailpipe. The 02 sensors look at these exhaust gases before and after the catalytic converter, the computer compares the values and determines if the catalytic converter is doing its job, if not... you get the dreaded P0420 code.
As far as a rattle, it could be a loose heat shield. You would have to visually inspect each heat shield to see which one is loose. Also shake the exhaust system slightly (when it is cold -- not hot) and see if you can duplicate the rattle.
As far as the car running rough, are you seeing any other check engine light codes?? How many miles on your Versa??

 

[Desert Rodent]

If the motor is shaking, the motor mount may be worn out. Visually inspect the rubber inside the motor mount for damage.

 

[Desert Rodent]

On thease cars what's the part I can replace to have it on smoothly idol I'm questioning??

If the catalytic converter is bad, which would make sense since you are getting a P0420 code; the substrate inside the catalytic converter may be clogged/damaged and may be restricting the exhaust flow out of the tailpipe. A restricted exhaust flow will cause the car to run rough.

 

[Desert Rodent]

Is it a tap, rattle or click?? If you are in park and gently tap the the gas pedal (raise the rpms, slightly) does the tapping sound speed up to match the engine rpms??
Try this... In an empty parking lot (at a slow speed) turn the steering wheel all the way to the right and make a circle, do you hear the tapping sound??
Now do the same thing, but with the wheel turned all the way to the left.
I am curious about the condition of the CV joints/axles. In addition to these "turning tests" can you visually inspect the CV joints/axles. Look for tears/splits in the boots.
It does sound like you have multiple problems with the car.

 

[Desert Rodent]

I think you need to take a step back and try to look at what the car is trying to tell you. There may be other little issues, but lets start with the big problems first. You posted a picture of two check engine light codes ==> P0420 and P0300
(1) Misfire - When you cleared the codes and drove the car, two codes came back P0300 (misfire) and P0420 (catalyst code) correct??
I think you should try to clear up the misfire first. Once that is resolved and fixed, then look at any exhaust restrictions from the catalytic converter.
There may be other issues with the car, but lets get the check engine light codes cleared first, then start working on the other secondary problems/issues.

 

[Desert Rodent]

If it is not illegal in your state, perhaps you could put an "anti fouler" device on your downstream oxygen sensor. They cost between $5-$20 and you'll also need a small tube of copper anti-seize compound for the threads. Between google and youtube you can learn about this trick. Again, in some states it is illegal... so you'll want to check into that.

 

[Desert Rodent]

So only downstream if I'm correct??? Can I use it for upstream has well it's a question?? Or only downstream

Only the downstream oxygen sensor... leave the upstream sensor alone.

 

[Desert Rodent]

Since I show you my codes on my car all ready what first I should start with what the adapter for the sensor downstream first .??

Based on your previous posts, I was under the impression you corrected the P0300 misfire situation and all you had left was the P0420 code. Is this correct??
The "anti fouler" trick should correct your recurring P0420 code, unless your catalytic converter is too far gone. (again if it is not illegal in your state to install that device on your downstream O2 sensor)
After installation, you will have clear codes, then the emission monitors reset to zero and start performing their self test. After driving a week or two (depending on your commute, etc.), you should have run most (if not all) of the self test emissions monitors.
Report back if the check engine light comes back on and what the next code is, if any...

 

[Desert Rodent]

The way I understand the catalyst system, the upstream O2 sensor obtains a value of unburned dirty exhaust gases (lots of unburned hydrocarbons, etc.). Just to make this example simple, let's say that value is 10, then the exhaust gases go through the catalytic converter. Inside the catalytic converter the unburned fuel and unburned hydrocarbons get burned. The precious metals in the catalytic converter burn and clean the dirty exhaust gases. When those gases exit the catalytic converter the downstream O2 sensor obtains a value, let say that value is 1, that would mean that the catalytic converter did its job and burned the unburned hydrocarbons. The computer in the car compares the upstream value of 10 to the downstream value of 1 and is happy as the catalytic converter did its job.
When the catalytic converter becomes damaged and/or overworked it can't burn those unburned hydrocarbons. When there is a misfire, there is A LOT of raw fuel in the exhaust gases, so the catalytic converter is pushed past its design limits and gets damaged from being overworked. With a damaged catalytic converter the downstream O2 sensor sees A LOT of unburned fuel and unburned hydrocarbons (going out the tailpipe) and obtains a value of 9, instead of a value of 1. Your computer isn't happy, as it wanted to see a 1 and saw a 9, so it throws a P0420 code telling you that it is upset with the amount of dirty exhaust coming out of the tailpipe.
By putting the anti-fouler device on the downstream O2 sensor you are limiting how much the downstream O2 sensor gets to sample, thus it gives an erroneous value of 1 back to the computer and the computer doesn't throw a P0420 code.

 

[Desert Rodent]

yes because I'm the morning I smelled alot gas but few minutes it goes away while the car is at hot temperature doesn't smell like gas anymore as well runs good

It takes a few minutes for a catalytic converter to warm up and do its job. The exhaust gases heat up the precious metals inside the catalytic converter and it begins to clean up the exhaust gases.
In the morning when you first start the car, the catalytic converter is cold and the unburned fuel and unburned hydrocarbons go out the tailpipe, thus you smell them.

 

[Desert Rodent]

Inside the dash area, there are blend doors and actuators that open and close based upon the temperature you set. If you are hearing clicking inside the car (dash area) as you change your heat/Air Conditioning requirements, I'm thinking there is a stuck blend door or an actuator is stuck and keeps trying to open or close.
I might try to stick my head under the dash (passenger foot well area), then have a friend change the heat & A/C controls and listen carefully trying to pinpoint where exactly the noise is coming from.

 

[Desert Rodent]

I think you need to isolate what sounds you are trying to fix. If the tapping noise is inside the dash (in the middle) start there and attempt to track down the noise by duplicating the circumstances (that cause the noise) with your head in the passenger foot well.
If your belt is squeaking/squealing, it could be the belt, the alternator or an idler pulley. You'll need to pull the belt off (inspect it) and inspect each pulley for wear (grinding sound or rough feel when turning).
If your motor/transmission mounts are worn out, replace them. Visually inspect them and if torn or worn out, time to replace them. Personally, I don't spray anything on my motor mounts, if they are worn out, I replace them as they are not all that expensive.
As far as a flywheel or flexplate, (personally) I've never seen one wear out. I have seen damage where a starter failed to retract and ground the teeth down, but that sound is an unique grinding sound (not a tapping sound).
You may have multiple problems with your car whereas there is no one fix. The tapping sound in the dash, may not be related to belt squeal under the hood.

 

[Desert Rodent]

idler pulley mean

If you are asking what is an idler pulley, it is a round doughnut shaped object that the serpentine belt or drive belt rides on. It is located on the belt tensioner. There are several items being turned by the drive or serpentine belt while the engine is operating. The alternator, the A/C compressor and the idler pulley on the belt tensioner. The pulley around the crankshaft is the work horse that spins the other items.
The idler pulley does have bearings in it that do wear out, then it will whine or squeal.

 

[Desert Rodent]

A flywheel is traditionally used in a manual transmission car, whereas a flex plate is used in an automatic transmission car. Neither has the ability to squeak, they just spin.
A bad motor mount will give you a "thunk" noise from time to time, as the engine shifts during acceleration (rotational forces).
Again, a good visual inspection of the motor mount is my suggestion.

 

[Desert Rodent]

There are plenty of "belt replacement" video(s) on youtube. In addition to checking the idler pulley, I'd check the A/C compressor and alternator pulleys for smooth operation. When you turn them by hand they should be quiet and not growling. They should feel smooth as you rotate them, if they feel sloppy... you found your culprit.

 

[Desert Rodent]

When not in use, the A/C compressor will "free wheel" (turn without a load on). When you turn on the A/C an electric clutch engages and turns the compressor.
It is possible that the bearing in the A/C compressor "free wheel" has gone bad. I don't know if that is serviceable or if you have to replace the entire compressor. (perhaps someone else on the forum knows).
As a shade tree mechanic, I tend not to work on my own A/C as I don't have the equipment to vacuum out the freon/refridgerent and capture it.
As far as the term "sloppy" for bearings and pulleys, you would be looking for side to side deflection or play when you attempt to twist the pulley from side to side. A good pulley bearing will glide smoothly, no noise, no grindy feel, etc. It will be silent, not growl or squeal. Again, there are multiple youtube videos that show you what is a good pulley bearing and what is a bad pulley bearing.

 

[Desert Rodent]

I have a manual tensioner on my 2016 Versa, I assume you have the same manual tensioner on your 2017. There is a gauge that you use to set the proper amount of tension on the belt. The pulley is a different part than the actual tensioner. There would be a bolt in the middle of the pulley that allows for removal and replacement.
Again, until you remove the belt and check each pulley, it is hard to say which pulley may or may not be bad.