My Yamaha THR10 amp sounds great in my apartment when running on batteries, but emits a nasty hum when powered by the power outlet in my apartment. I've tried turning off all lights and appliance in the apartment, but the hum is still present.
I'm not sure how to fix this -- are there hardware products that could "clean" the power from the outlet? Or might an electrician might be able to solve this somehow? Or is there some testing or maintenance of the electrical system in my house that I might do?