HU, analogue like crackaling n hissing

Hey there all, Headunit runs alright for 10 15 mins, at 80 - 95% total peak power output, then starts to play out hisses and crackles to the point music becomes intolerably annoying. The hissing sonds strangely analogue, like im playing a real bad record player. It fine at first first 10 mins, and slowly gets worse from to by 20 its just ARRRRRGH! If its the HU then no worries as its a cheapo panasonic (not that Panasonic aren't gd, there new HU look da dogs) But i've been reading up and come across something called Feedback noise or somen. Could this be the problem? Please enlighten !

At 80-95% you may be sending a clipped signal from your h.u's amp. And action1978 is right that heat is a likely issue here due to the clipping.

AAAh, a combined let down from heat resulting in clipping. WOuld a new (better all round) headunit solve this all? WHats causing the clipping?

Playing the volume too loud.Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

ROllocks! what? TOo loud? AH well, budget HU, budget sound grumble grumble grumble