Some of the old Kenwoods used to have trouble with the delay cap in the
protect circuit, leaking. As the problem is intermittent, might be worth a
look, but otherwise, as others have said, good first place to look is at the
speakers and their wiring.

Arfa
I'd go with the delay cap too. Isn't that typically a low value
electrolytic in the relay turn on circuitry?
Jango.