Guitar Amp Squeal?

[Dave71]

Borrowed a Boss Katana 100 last night for a one off gig and got there nice and early to set the amp up. Took my gear into a side room and started to dial in some settings. Sorted the clean channels then as soon as i tried to set a crunch/drive/lead channel, the thing started squealing terribly even on low volume. Was using a USA strat and found that the squeal was in all 3 pickups but not when in the out of phase position - was under the impression the pickups were microphonic

Swapped leads and guitars (another USA strat) to no avail. Line check time soon came round so had no option other than to setup on stage and try wing it until our other guitarist arrived with a his spare amp and guitars.

Turned on, turned up quite a bit higher than in the side room grit my teeth.....and not a squeal - ran perfectly all night.

Any ideas on what could of caused that? Room power issue?

[Murray B]

I had a mystery very high pitched feedback issues once, I finally figured out it was being caused by the venue's loop system for hearing aids. The single coil pickups on my guitar were picking up the signal from the loops system and with enough volume created a feedback loop. Once the loop was turned off - problem solved.

Maybe this was your cause, rather than the change of amplifier, but I couldn't say for sure.

[Dave71]

Ahhh…that may of been the case, it was a community meeting room and I suspect they have loop systems in there. Good shout.
Forgot to mention I was listening to a Beyoncé track, Crazy in Love If iirc, through my guitar at one point.

[Murray B]

It's only ever happened to me twice - second time around I knew how to solve the problem straight away and avoided the 40mins of head scratching during the soundcheck.