Hello,

I've got an AVIC-NEX 8100 installed in a 2008 Porsche Cayman S. I'm experiencing some alternator whine (I think) - sounds like a high-pitched frequency that matches my revs. The conditions that I hear it in are as follows:

With any volume on (low volume, high volume), the whine isn't there. 

As soon as I mute the system with the car on, there is a period of about 5 seconds where the system is dead silent (no noise from speakers and no whine)

Then, about 5 seconds after muting, I hear a white noise sound come on and the whine is audible. 

Any ideas on why I would hear the white noise sound 5 seconds after muting or turning volume to 0, and why this is the only case in which I hear the alternator whine?

Many thanks.

I'm assuming the porsche has a factory amplifier that you adapted the radio to.  This is a common issue when adapting to a factory amp, my dad's xterra had the same issue.  We used this to fix it:  https://www.amazon.com/Monoprice-106909-Channel-Ground-Isolator/dp/B004C4ZNNO/ref=sr_1_8?ie=UTF8&qid=1493057347&sr=8-8&keywords=ground+loop+isolator

try to set the brightness to max of the headunit, and see if it still hums, some people hear that kind of noise because of the pwm backlight.