I dont know if this is the same problem (and its not the same cab as im in UK and it was a NYC cab) but i had a "noise" coming from inside my 112NYC cab when i played lightly, over the neck or front pup on my B string around the 5th fret. there was a lot of bass of course but the volume was very low. I never did figure what it was but took it back to the shop anyway. playing "normally" with the lows backed off a bit, around 1o'clock it sounded ok.
This has put me off getting a UL112 though. i cant understand how you guys get away with using them with 5 string unless the cab was defective. Even playing the same way through the same amp in to a Ashdown MAG C-115 speaker didnt produce this effect so it might have been the cab.
Sorry to go OT.