???

ok all of a sudden my 1998 lumina is making a weird high pitch noise and it comes from the rear of the car. I really comes on when I have the heater or front/rear defroster on but it also comes on when I just have the car on alone just not as bad what should I do. :mad:

ok all of a sudden my 1998 lumina is making a weird high pitch noise and it comes from the rear of the car. I really comes on when I have the heater or front/rear defroster on but it also comes on when I just have the car on alone just not as bad what should I do. :mad:

Well, that's a tough one. Whatever it is, it sounds like it is reacting to the amount of load on the electrical system, as both those items are among the highest current draws on the car. My only guess is that you are hearing a fuel pump that is starting to go bad, and the change in electric amperage available to it changes the intensity of the sound.

Do you hear it if you just turn the key to on, without starting the car? If it is the pump, you should hear it for a couple of seconds as it brings the fuel pressure up, then stop, happening again after the motor is started.

Try that, see what you notice.

If the sound is comming from the rear of the car, it could be the fuel pump. I have heard some real noisy ones, even when the car goes down the road past you. Now here are some of my other thoughts, when you have the ac/heater on, could it possibly be an air leak out of the car, maybe the rear window is open just a crack, or someplace else the air is leaking out? If the sound was in the front I agree it could be the alternator, with varying loads.
If the car was a Ford,(LOL)it could be a whistle coming out of the air intake. Have 4 Fords, all with 4.6l engines that whistle when it's really cold out,goes away when it warms up.