Amp problem - Sounds drops out of one channel

Related to my other thread where I mentioned my amp needed repair...

I've got a Classe CAP-100 which I'm using to drive Revel M20 speakers.

I've recently been having trouble where the volumne in one channel drops out significantly or entirely at low listening levels (I live in an apartment and most of my listening is at low/moderate levels).

If I turn up the volume control the sound will return, but when I turn the volume back down to normal listening level it will eventually drop out again.

It can happen in either channel, regardless of source (CD or turntable).

Anyone got a clue what this might be? Also, does anyone have a recommended stereo repair shop in New York City? I bought the amp secondhand from an out-of-state dealer years ago. I'd rather not ship it to Classe in Canada if I can get it fixed locally.

Thanks in advance!