Never had it do that before, but yeah I guess I will there, no harm in taking the cover off at this point (although sometimes I am apprehensive to do so with some equipment lol)
I wonder if I can get another coworker to give it a shot in their setup, but a modern apartment building or especially office park is where I would expect big issues to also arise in, but yeah worth a shot.
I would just want to make sure it was a pure sine wave generator, and to be honest most of the quality of output of those are pretty garbage or potentially unsafe for some electronics. I could take it to a nearby data center and hook it up to an online double conversion ups or flywheel I guess, that would maybe be a safe bet to test
DC is the usual culprit for physical hum. Isolation transformers remove that.
But I’ve had new transformers that do it even when I know there is no measurable DC on the circuit, and even when connected through an isolation transformer. Though it tends to be higher poered devices that really suffer from this, seems odd to have it on a DAC.
It’s most likely movement between the plates in the core of the transformer, though it can just be the transformer moving against the case, DC makes that more likely, but sometimes it’s just a poorly manufactured transformer, the bolts are loose, or in some cases just shipping it causes resin/wax material they encase them in to just not hold up well enough to stop it.
Tightening bolts won’t hurt, and even if that doesn’t resolve it, it’s unlikely to be a problem for the device outside the hum itself.
Could also get a synchronous motor generator set, they are an old-school (and noisy, and inefficent) way to get total seperation from the power grid. The only link to the outside world is a spinning shaft between motor and generator.