I just bought a sentra se-r and the motor in it only has 40k miles...but. There is a slight noise coming from the left side of the motor kind of where the pulleys are. It doesnt sound like knock more like gears grinding like the water pump gears are going. The guy i got it from said it was one of the pulleys wobbling. I'm planning on boosting the car and I dont want to throw a rod or something so if anyone could give me input of what it could be so I can check it and fix it.