Following a series of electrician induced power failures (*) yesterday afternoon the audio output from my PC now has severe mains hum on it. I have a Arcam Alpha 9 plugged into the 3.5mm headphone socket on my Dell Inspiron machine. I use this a lot to listen to music in the study. It's not the amp - I've tried plugging the audio feed into another source and it's fine. The PC is protected by a UPS, so won't have gone off while the sparks was doing his thing, but the amp isn't, so it will have been switched off and on. I've made sure everything's properly plugged in, which it is, and the hum's definitely coming out of the PC. It doesn't vary with the volume setting on the PC.
So ... where do I go from here? I'm not even sure how to go about diagnosing this. Any suggestions?
And while you're thinking about this, perhaps someone can suggest what we do about the nuisance RCD trips which were the reason the sparks was here. Two of them have spent several hours each testing things, and both times it's "no fault found". The best suggestion so far is to swap out the CU for one with RCBOs, so (i) the earth leakage will be spread across a number of devices & (ii) at least we'll be able to narrow it down to one circuit. We presently have a split CU with an RCD on the power circuits and nothing on the lighting. We're getting 2 or 3 nuisance trips a day at the moment.
(* "I'm just going to run some tests" "Do I need to switch off the PCs?" "No, that'll be fine" [Electrician, or at least his test set, then proceeds to switch power off and on about 4 times in a minute.] Sigh.)