There are a few things that can cause feedback so it can be tough to figure out sometimes. I was getting some microphonic feedback a few years ago on a guitar and it was the pickup. It needed to be re-dipped in wax to get rid of it so I just said screw that and put a new pickup in it. I believe the process is called "potting" the pickups and it is usually done by dipping the coils in wax or wrapping them in tape. Pickup height can certainly make some feedback problems and I thought you could adjust the pickup height on all the JPMM guitars, but I'm not certain, maybe some of them have mounted pickups? It sometimes is just where you're standing or sitting when you play, or even the room you are in, or it can be that you have too much gain on the amp. Will take some experimenting to figure it out possibly. Good luck.
