Hum!!

George Meyer, A/V repair expert, located near Santa Monica, or west side, they moved recently. Very good, very reliable 

Good luck,
Bob

call them quick

if it is the power supply caps, they may blow and wipe out the entire amp, maybe some drivers too...

@stereo5
+1 for wit

Here’s a lovely story for post holiday enjoyment: A hum appeared in both my subs, which are RELs connected to a single ended amp (Inspire Fire Bottle HO) with Canare wire attached to largish spades to combine the cables…works great. I take the cables apart at the spades and re-do them, look at the Neutrik plugs at the subs, tighten everything, check all the AC cables for grounding issues…basically take the whole gear heap apart…still humming…low frequency just going on and on...go through the amp tubes (there are only 4 on this amp so no big deal)…KT88s swapped out for others, 6SN7GTB swapped for its backup…no change...I get to the rectifier, a 4 month old Gold Lion GZ34 and BINGO! Swap it for a 274B I had in reserve and the hum disappeared. The end.

@stereo5 Nope. Dry. As in it has "dried" out over the years from not having the flux flow properly and cracked. Cold is a faulty solder joint from the start by not having the iron hot enough. I said connection instead of joint to help clarify in case the OP was unfamiliar with the terms.