My 2010 versa has a knocking noise. It has about 5900 miles on it, all interstate mileage. It started about 1500 miles ago - the dealership (well, one) stated it was just a nissan. Another said it was "cheap gas" - even though I've only used cheveron or bp. This past weekend, I lost almost all power - I literally had to floor it to keep speed up a slight incline. I have to floor it to get speed on the interstate. Could it be bad gas? Its rather annoying to drive now, and it's really pathetic that our other vehicle (05 focus with 130,000+ miles) drives better and sounds much better than a new car. Any suggestions would be appreciated!