Noise when plugging in fan

SpikeyMcSpikeFace

Ok, random question, but it's doing my head in ...

For years I've always used a fan on-stage (cos I'm sweaty ...!). I've never previously had issues, but recently in some venues I'm getting a hideous buzzing noise through the amp if I plug the fan in to shared mains (eg. via a multi-way plug cable) alongside the power to my pedal board (which is powered by a GigRig Generator plus separate isolated DC feeds to each pedal - it's as quiet as the proverbial). Sometimes if I power the fan from another plug (eg. run an extension from the back of the stage), then it's fine - but not always (I guess it depends on how the venue's stage power has been wired).

I've had the fan checked over by the guy who does my PAC testing - he upgraded the plug, checked everything else, and all seems fine (no dodgy wiring, etc). And nothing has changed in my live rig (same FX board, amp, cables, etc). So I can't fathom why this has started, nor what to do about it (last couple of gigs I just had to turn the fan off ... and get uber sweaty ...!).

Any thoughts / suggestions ...?

Thanks.

ICBM

The motor suppression cap has probably failed. This won't be obvious from either a visual inspection or a PAT check.

SpikeyMcSpikeFace

Thanks - that's really helpful, nice one.