so those caps being bad is causing your issues, because with out them, your mac backfeeds noise onto the ac line?

pretty interesting.

i would get a inductive current meter, here you can buy them for like 7 or 8 bucks at harbor freight.

open your Breaker box and see how much current is flowing through the breaker your on, maybe half the house is on one breaker?

Maybe you have special breakers installed? ones that are stupidly sensitive by design to detect such feedback.

Post the model / name of the breaker on your circuit? maybe a picture of your breaker box?