Power amp humming - help please

If the hum is physically coming from the amp, specifically from the power supply transformer, that is DC offset hum. This is eliminated either with something like a Humbuster power strip, or by trial and error to find what is plugged in or wired that is causing the offset. 

If the hum is heard to be coming out of the speakers then this is ground loop hum. 

So as usual we start with precisely identifying exactly what it is we are talking about.

Gong, is the hum coming from the speakers or the amp directly? If it is coming from the amp directly then I agree, it is most likely the transformer. If it is coming from the speaker then you probably have a ground loop. Try putting a ground "cheater" on the amp's power cord and see what happens.

The volume doesn't change when I crank the volume up on pre, if that means anything...

mijostyn, excuse my extreme ignorance on Hifi, but how do I put a ground cheater on the amp's power cord?

The hum is coming from the speakers and not the amp, mijo...