I have an ESP LTD Viper-50 (lame, I know). Playing through a Either my Crate 120 combo,or my Dad's Randall 200 Halfstack, I get ridiculous amounts of feedback, no matter the settings. Playing through my Kustom Dart (15 watt) even on high volumes, I get no feedback. Could it be the high gains of the bigger amps? Or maybe a wiring problem with this model?
Try turning the gain down and standing a little farther away from the amp.
I've actually tried that. The only place it's feedback-less is not quite directly behind it, but off to the right (if you're looking at the front of the amp)