zigwizard

I'm experiencing a high pitched whine that increases in pitch with engine RPM. It stops when i turn off the head unit. I'm not sure if its a head unit issue or perhaps something with the system voltage regulation. I checked the fuse for the sub which had blown - I replaced it and checked the sub and amp which work fine on an alternate audio source but no response from the head unit. Any ideas?

99 A4 1.8TQTip

MacSub

I'd start by adding an addition earth lead to the chassis of the HU, short length straight to the bodywork.
If it's an aftermarket HU, then it depends whether it's a Bose system (whine from all speakers) or non Bose - whine from just the rears.
With the Bose system you're screwed. Non Bose, just rewire the rear speakers directly to the HU as the rear amp is not only feeble but also wired badly and this will pick up interference. Bose has a seperate amp driving all speakers and you can't easily by pass it as the speakers are 2 ohm and sound dreadful without the Bose amp.

AUDI GT1

put an in line resistor on the speakers should clear it up if not the head unit? / blown amp the old head units did this a lot.

MacSub

Think you mean inline capacitors mate! Not really the way to go as you'll loose top end frequencies