So I've got this n/a 1991 740 wagon that's pretty much all original. Yesterday it wouldn't start for some reason, but it started fine today. It's been acting normal all day, except I gave my friend a jumpstart and ever since then it's been making a terrible whining noise through the stereo.

It definetly changes pitch as you rev the engine up, but it doesn't change volume when I change the volume on the stereo, and it makes the speakers sound like they're breaking up. It still sounds bad even when the engine isn't running, just not the whining part. Out of curiosity, I pulled #26 fuse, which is for the amplifier, and when I do this the noises all go away. You can hear that the audio is much clearer, but very very quiet.

Is there any chance that the amplifier got fried because of the jumpstart, or do you think it could be something else?

thanks!

(had to make a new account because I haven't been on here in years and forgot my password....)