I should provide a few more details on the Amp, and clarify what I mean by "clipping". It is not clipping in the audio term (when you turn the sound up above what the amp can handle). I believe it is the toroidal transformer making a clicking sound (it always does when I first turn it on). When it makes the clicking noise the audio stops for 1-15 seconds.
What you are describing sounds like a power on muting circuit. You should stop by the audio shop again because any decent one will have a variac to troubleshoot with. Start out at 120VAC and slowly work your way down to the lowest voltage that the amplifier is specified to. There is quite possibly a muting level adjustment in there. Toroids hum because they forgot the words. Relays click because they are holding one supply down while waiting for others to stabilize or shorting inputs to protect speakers and ears. I'll hold my tongue on some of those specs. If you can't get to a muting threshold adjustment, a properly rated variac locked down to 100+% would probably be the cheapest solution. Now, if you happen to have the schematics...
Joe
