High Pitch Interference through monitors

[MisterE]

We moved to anew location for rehearsals and I noticed a high pitch squel (like feedback) through my CLR's.
At first I thought it was my guitar that created the feedback, but I had it with all my guitars.
Moving the CLR's to the back didn't solve the problem, neither did lowering the volume.
I noticed when unplugging the guitar cord and torching the tip, instead of getting the ground hum, I got the high pitch squeal as well.
Plugged directly into the CLR's - same thing.

I took the CLR's home and there I had no problem.
I could hold my guitar with the volume knob open at 1m from the speaker at high volume without it feedbacking one bit.
Plugging the guitar cord in the CLR and touching the tip didn't produce the squeal but the 50Hz hum.

So there must be something wrong in our rehearsal room.
Could something electrical be causing this?
Ground problems?
Wireless interference?

And the main question - can this be solved by using a power conditioner ?
I have a APC Line-R but I 'm not sure that'll do the trick.
I'll try it anyway next rehearsal.
But if you guys have any ideas..

 

[Dutch]

Slow weekend...

Don't have CLRs. Sorry. But I did get some odd sound out of my dBs once. Or twice. It could be magnetic interference of course. We play in churches, whenever there's a hearing aid system (induction loop) it needs to be shut down. Something similar might cause this. However it usually works on the pickups, not on the amps.

Dunno. Please try the APC and fill us in?

 

[MisterE]

Tried the APC. Didn't work.
I put a filter block with a notch filter and found out the interference is at 3.2kHz
No domotica installed.
Only a very powerful wi-fi access point from a nearby neighbour (400m) but that works at a much higher frequency.

 

[MisterE]

Could this be caused by a radio signal for a robot lawn mower?
The squeal is around 3.2kHz