Help my Raven Labs APD-1 is buzzing

[WorBass]

Does anyone have any suggestions for figuring out how to stop my APD-1 from buzzing? It's not horribly loud, but not acceptable for a di of that quality. I plugged into a whirlwind di and the buzz went away, so everything from the di on was OK. Full charge on the batteries. Happens on both ground settings.

Any wisdom or insight would be greatly appreciated!

[bongomania]

Hard to know for sure what's happening by long distance, but my first guess is that it's old and a solder joint that wasn't great in the first place has finally cracked.