Have you tried lowering that slanted pickup?
A power conditioner isn’t going to fix this.
Plug your guitar straight into amp and bypass pedals. Feedback? Does another guitar get feedback straight into your amp?
Plug your guitar into a different amp at the volume you play at. Feedback?
This should tell you whether it's the guitar or the amp.
If neither test indicates a microphonic guitar or a microphonic amp you are going to have to sub out your cables one by one and test your pedals one by one. Then in pairs, etc.
You have to isolate each component one by one.
Bill
If it feedsback with your buddy’s amp too then I guess we can eliminate the amp as the culprit. Do you have another guitar to try as well? Or does your buddy’s guitar feedback through your rig?
Fwiw, I have a LP Special p90 that I had put a Tone Zone p90 humbucker in and it was doing the same thing. It made the guitar totally unplayable. I could have never used it at a gig. I even emailed Dimarzio about it and I sent it back to them for repotting, which didn’t help. It didn’t matter how low I adjusted the pickup either. It just didn’t work in that guitar.
Last weekend I took it out and put the stock pickup back in and all is good.