I just purchased a used 1998 Custom 22 with the Dragon pickup in the bridge and a I also own an Ibanez JS2410 with the DiMarzio Mo' Joe humbucker in the bridge. Plugged into the same rig/pedalboard with medium-high gain settings the PRS produces significantly more hum than my Ibanez (could be described as a high-pitched screeching noise, especially when I turn on the wah). I've tried lowering the bridge pickups slightly but there's still significant hum coming from the guitar. No problems with the neck pickup though.
Would appreciate if someone more knowledgeable here could help me out with this - could it be an electronics/shielding issue in my guitar?