tested the alternator and the voltage is good but diodes are broken which could explain the turbo whistling sound, getting a new alternator Friday as this one is the OEM that has lasted 20 years lol, will report back!

Broken diode is the usual cause of your symptom.

Alternators generate three phase electric AC and that's converted to dC though a 6 diode bridge rectifier.

When one or more of the diodes fail (usually open), you'll get lumpy 2 phase power. This will give bumpy torque at the drive belt causing vibration.

It can also cause electrical interference that you can hear in the stereo.

this explains my speakers randomly getting low at times on certain sides of the car, I'm getting the Valeo style 12v 140amp alternator installed Friday

I'm just surprised the voltage is still good after all those years but oh well I guess I got my money's worth


Sidenote: got the classis engine failsafe error tonight after leaving the gym, turned the car off and waited a bit to restart, started her up and bam everything ok, I think this might be a good sign alternator is starting to take a shit lol

alternator was the cause of the whistle noise, replaced a few belts as well, running like a champ now, however on the prowl to maybe sell since I think it's time to move to an X5M :)

so I found mint condition 4.8 mufflers, might pull the trigger on it, I can sell my 4.6 cans on here if anyone would be interested?

can you post or dm me a clip of your 4.8 mufflers on your 3.0i?