Occasional hum

[CageyH]

The hum continued, although it was not as noticeable.
I think that during my desperation to fix the issue, I ordered some generic UF4007 diodes to replace what may have been faulty parts to rule them out.
These have now been changed out for Vishay SF4007 and time will tell if the generic Amazon supplied faults were part of the problem.

[CageyH]

The problem continued, although not noticeable when music was playing.
I have fixed the issue by conditi9ning my mains through an Eaton 9sx UPS, which provides a pure sine wave.
My Power Inspired AG1500 seems like it is broken, as when I tried it to power my BB3, it was blowing the fuses in the BB3 on power up.
I have not had a chance to look at the AG1500 yet, but due to the age, it could be one of many things.

Even though the Eaton 9sx is a good unit, a word of caution - the fan is very noisy.
Mine is now modified with a Noctua fan, but it is not a straightforward swap, as you also need to fool the fan monitoring system, otherwise the UPS will stop,working due to the protection circuits.

[Barry]

Your "occasional hum" problem is certainly giving headaches for you Kevin.

I think you said you thought the problem might be due to a power-hungry industrial plant nearby. If it is, can you not complain to EDF and see if they can help. Certainly in the UK, if a neighboring industrial user causes problem to domestic users, the local electricity supplier will ask them to fix the problem. I speak from experience, as the arc-welding unit of my father's business was causing a phase shift of the domestic monophase supply (and hence poor power factor), that he was obliged to have a phase-correcting capacitor fitted.