I'm getting some feedback when I turn my amp up past a certain volume. I'm not sure what's causing it, so here's my rig. Maybe someone can help me out.

'72 Telecaster Reissue
Digitech GSP1101 Rackmount Preamp
BBE Sonic Maximizer
Orange Tiny Terror Head
Orange PC212 Cab

Any ideas would be greatly appreciated. Thanks!!
that could be it. it's doing it whether I'm facing the amp or not. would it still cause feedback if the pickups are facing the other direction?