Power amp humming - help please

Right!!!

Test the amp with a cheater plug, an adapter which removes the ground.
https://www.target.com/p/general-electric-2pk-grounding-adapter-polarized/-/A-14442316?ref=tgt_adv_X...

If it removes the hum then you have a ground fault somewhere.

Thanks so much lowrider!

I ordered it.

Later, please help me find the ground fault - I have no idea how to do that - excuse my ignorance on electronics...I just love music.

The cheater-plug will help troubleshoot the hum. If the hum stops when it’s plugged in then there’s a ground-loop.

To review, you disconnected all audio cables from the amp and you plugged the amp into different receptacles.
It’s possible they may be on the same circuit. Last thing to try, plug the amp into the refrigerator or air conditioner receptacle. They are possibly on dedicated lines, different circuits than your audio system.

Do you live in a house with your own service panel (circuit box)?