2004 TL 128k with nav

At around 110k I started hearing a buzzing from the center dash speaker after starting the car. After driving for 30+ minutes it fades away.

There is no buzz with stereo volume all the way down or stereo off.
Sound is present regardless of discs in CD player or empty, radio or xm station, AC on or off.

Buzzing NOT present when engine off and ignition turned to on.

Thoughts?

 

Your amplifier is bad. You can get a used one on ebay for around $70. I think they are the same for all 3G TL models