If you get hum from more than one component/brand, there's every chance of finding a solution to the problem. In your case, with the silent-running Pass, I'm not so sure that these bandaids (e.g. DC blocker) will make any difference. There are lots of threads of this sort. I myself have been through this wringer (and I ended up buying different amps). I wish you luck and success but be prepared for no easy fix.
ATI AT6007 amplifier hum
Long time reader and first time poster. I recently traded in my Pass Labs X600.8 amps to ATI AT6007 and AT528NC combo for my 9.1.4 setup. I have 3 dedicated 20A lines which I’ve used previously for the pass labs and now for the ATIs. I did not hear a hum from the pass labs but I’m now hearing a hum from the AT6007. I’m also using proper 20A power cables. There is no hum from the AT528NC. Please advise. Will I need a DC blocker or power conditioner?