It's a component overheating. Expose the circuit and touch each

component with a cool Qtip that has been dipped in alcohol (not

dripping, just evaporating). The overheating component should reveal

itself. Remove and replace.

I doubt that replacing the heated component will cure the problem. You would best find out why the component is getting hot in the first place. A defective speaker can cause this by providing too low an impedence load on that side of the amp. Try swapping the two speakers first. If the problem now occurs on the opposite side, the problem is the speaker not the receiver..

Dan