I’m currently experiencing a similar problem with a tube preamp and a tube DAC. Both were originally wired for 220V and were dead silent when running on said voltage in Europe. They also worked fine via at step-up transformer after I moved myself and them to Canada. They have since been converted to 120V operation via the manufacturer’s instructions with work performed by an authorized shop, and now they both buzz like crazy from their transformers. And it does seem to cycle between a loud buzz to a relatively quiet one over several minutes, perhaps similar to what you are experiencing.

I’ve tried a DC blocker (Ava Humdinger) and an isolation transformer (Decware ZLC), but neither one helped. I will try a UPS next just to completely rule out any issues with the mains supply/household wiring. Otherwise it’s back to the shop with them…

Hope you get yours sorted. Please be sure to report back if you do.

Yeah I definitely agree with that. The room was originally painted white and the overhead lights seemed less harsh at that time. With the black walls they’re now quite annoying, so I tend to just have a few lamps on when actually listening to music.

Rate my dreary mancave.