So, weird problem...my backup 7-string had the stock pickups from an RG7620 in it. I was having all kinds of microphonic/squealing problems with it, making it almost completely unsuitable for playing live. I replaced the bridge pickup in part because I figured that it would solve the squealing problem.
So tonight, I took the guitar to band practice, and had squealing problems with it. I tried it through both my amp and my bandmate's amp, and then tried the other guitar I had with me through my amp, and the 7 was the only one having issues.
What could cause this noise? Pots? Switch? Output jack? Something else entirely that I'm not thinking of?
Roll the volume knob down some, happens often with hot pickups.
I run my volume at 2/3-3/4 full to stop the squeeling.