So ive been having this whine in my car for a while now. It gets louder/worse when the electrical system is under load (heated seats, stereo, headlights etc) and it varies in pitch with the RPMs. I finally took my car to autozone and had them test it and it gave back a reading saying the diodes were bad. Ive been driving it for a couple months with this noise however and ive never had it not start etc, and the battery according to the lady that tested it was 100% charged and healthy.

Based on my hunch and the readout from the test it seems like the alternators dying however I figured id ask and see if anyone here had a second opinion.

 

When I had my AC compressor replaced, the new module would whine. Although mine didn't correlate with the electronics at all.

Just for funsies, turn your AC setting off, do you still hear it?

 

Yeah it still whines with the AC off, Im pretty convinced its the alternator as according to service records its the original that came with the car, so its going on 14 years old

 

Did you do any changes to your audio system? A bad ground can cause alternator whine from the speakers. Or is yours coming from the engine bay?

 

I'd like to add onto what Eddie said, I have my CB radio (straight out of the 70s.) that likes to whine when I am accelerating and have it on. So, if you have added any electronics, they just might not be as good of quality to compensate for the inconsistent voltage.

 

its definitely coming from the engine bay. I have an aftermarket stereo receiver but thats the only change and it was with the car when i bought it and the whine wasnt present then

 

Well that's weird. I ran an external amp with my stock alternator and it still doing fine. How loud is whine? I'm adfraid that your it shot. Double check everything, maybe a bad ground if not you need to get it replace.

 

The whine was pretty bad and obnoxious, much worse inside the cabin than outside though. I ended up taking it to the mechanic and we stood around the engine bay for a good while trying to figure it out. Battery was fine, it was charging fine and the volts were right. My hunch told me it was the alternator so I had them replace it even though they werent 100% sure, and it fixed everything, no more whine