Just had this squealing sound all of a sudden, pretty much on the decay of an open chord suddenly muted, but I can hear it subtlety through everything. I've attached a recording, I pushed the gain to 10 half way through just to exaggerate the noise. Happens on 3 different guitars, all outputs, 2 different wireless setups (all my spare leads are in the roof). It's the same slightly sharp "C" note no matter whether I play an open d or an open a.
Any ideas?