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Alternator whine


24 Oct 2014
I've suddenly developed an alternator whine which means I have to keep my stereo (original head unit and amp) off to avoid broadcasting my engine noises! 2004 996 C4S.

The only recent changes of note are:

1. Had car restored recently including removing front quarter wings, cutting out rust and welding in replacements etc.
2. Had my alternator refurbished recently and installed it myself.

I've been looking into the problem a little including the possibility of a ground loop isolator (as a quick fix) but I'm not great with wiring/electrics.

I've been in touch with a car electrical expert who thinks the alternator is a possible culprit and wants to test it. It otherwise works perfectly.

Any thoughts gladly received. It doesn't look like an easy fix and i don't want to spend loads on diagnostics.

My 996.2 with Bose also whines when stereo on however my source fault is the Mr.Bluetooth module. Not an issue for me as I don't listen to music in the car but annoying when using Google maps!

I suspect I need/you need a ground loop but I don't know what to buy or where to fit and use the car so infrequently that I have not bothered to investigate so I am taking an interest in this thread bud...
Hi, I have the same Bluetooth module too but I never used to get the whine and I also tried removing it to no avail.

On the one hand, I'd like to be able to leave my PCM on, as I also have a SIM card and stream from my Spotify. On the other, there could be several hours of diagnostics needed to find the source of the noise which probably isn't worth it?!

My money's on a poor/missing ground secondary to bodywork?
Hopefully someone will provide us both with a solution!

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