2000 Boxster S radio buzz as RPM rises
 

My aftermarket Pioneer headset was stolen from my Boxster S. I had my shop replace the unit with another Pioneer new unit. Now there is a buzzing coming from the speakers especially as you drive more. So more noise with more RPM. The shop is highly rated and suggested my amp might be bad now, since the factory amp is still being used and not the amp in the aftermarket deck. Appreciate input.

The noise you describe is almost always caused by a bad or intermittent ground. Start by checking the ground wire (black) on that new head unit first since that's the last thing messed with.