So I just bought this Jackson a month ago http://www.sweetwater.com/store/detail/SLATTXMG37/. I ran into my 5150 III and it had a crap load of feed back, at such a low vloume. So I tried it on my Mesa Duel, same thing. Then my orange, and same thing.....
So I tried my other Jackson on all those heads and no feed back. Im not sure what would cause this. Its the only issue Im having with it, other then that its uber sweet. Any feed back will help..

Well I don't have any experience with a 7 string, there are days I have a bad enough time with 6... But, if this is your first 7, I would think that the larger pickups have more mass and would feedback easier than the six string ones.. Maybe cut the treble back a bit and see if that helps any..

_________________
Chaos, panic, and disorder.. My work is done here.