Audio issue
 

I have a new-to-me 2002 Boxster with the 490 stereo. The dash speakers work early in the morning but won't play later in the day. All I get is door speaker. I assume it's the heat of the day causing issue with overheating. Anybody know how to narrow it down to the amp or head unit? I tried placing a fan on the amp for a few minutes this afternoon with negative results.