The isolation transformer did fucking nothing and having the amp connected by aux made the speakers buzz constantly. Decided to connect the amp by optical cable instead so the digital/audio conversion would be handled by the amp away from the PC and it's fine. No more buzzing and no more startup ear rape. I think the ear rape was completely caused by the dollar store power strip.

RT: https://poa.st/objects/cfc11431-a58d-480a-ab4a-decc19f56b03