I have a Pioneer Spec 4 amplifier that I need some help diagnosing. It has been recently recapped including the big filter caps and boards. I am looking at it for a friend of mine and I did not do the work on it. The problem is it sounds great for about 10 minutes and then out of the blue a LOUD ARCING noise or extremely loud POP will come though to the speakers and scare the crap out you. Loud enough for me to turn it off without hesitation. It happens with no warning. I checked the DC offset and it is fine when I first turn it on. The relay clicks in nicely. It sounds great, for awhile. Is this DC current hitting the speakers after is in on for awhile? What would cause this? Anyone have this problem before or know where I should look first without throwing leaves to the wind?