buzzing from speakers

Recently picked up some used gear to assemble a decent, little condo system.

Recently noticed buzzing coming from the speakers when no music is being played. Thought it was speaker cable picking up hum from all the other cables strewn behind the wall unit, but after testing, that is not the case.

I'm concerned that the static electricity in my apartment may have damaged my amp somehow. I notice that almost every time i touch my equipment, i get a mild shock (because of the dry air in my condo coupled w/ carpet).

Could this have somehow damaged my amp /created this audible hum? I never noticed the hum in the past when i first picked up the amp, so i'm not sure if the problem has been there then entire time or if it's new.

Any thoughts?