What causes noise?

Maintenance/Repairs
1

I have NISSAN ALTIMA 2001 and near 100K miles. I’m third owner of this car since last May.

After oil change, the store recommended change of transmission fluid and CV axle boot. I did it. After that, It makes noise(like gas leaking noise) when the speed is higher than 60miles. The noise seems come from the back bottom of the car. The frequency depends on the speed, the quicker, the more often and the louder. It just happened 1 week ago and never happened before. Could anybody here tell me what’s the problems? My friend guessed that it may come from engine or air conditioner.

2

If it’s at the rear of the vehicle, it’s likely not the engine or A/C. Have you been leaking fuel? There’s a few things I can think of that may be the source of the noise:

  1. Rear tires - they may be unbalanced.
  2. Rear parking or service brakes - they may not be disengaging completely
  3. Something else vibrating - in the trunk, or trim piece, maybe it’s vibrating in sympathy with something else.
    Other than that, there’s nothing in the rear that would make a noise dependant upon speed. Good luck.
3

As was said, since your engine and all of the A/C components are under the hood, it is not possible that they are the source of a noise under the rear of the car.

I am not quite sure exactly what the source of the noise is, as this type of thing is very difficult to describe in words, but I do have a possible source for you. Have your fuel pump checked, as that is at the rear of the car, either inside the gas tank or adjacent to the tank. And, the speed of the fuel pump is directly related to engine speed, so it is possible that faster driving could lead to more noise from a failing pump. I know that on my crappy Volvo, the fuel pump frequently did make a lot of noise prior to dying (which it did about once a year).

If it does turn out to be the fuel pump, you should also be aware that this failure is not related to the work that was previously done on the car, and instead is simply a case of the pump wearing out. And, if it wore out at about 100k, that is pretty good compared to the 10-12k that I used to get out of the fuel pumps on my Volvo!