Sorry I have responded sooner on this- Turkey Day and all...

Car setup:

-3L forged internal ADC T3/4 60 trim
-SVT Lightning MAF, as required by ADC
-42lb/hr injectors from SVT Lightning, as supplied by ADC
-ADC chip for turbo kit
-Return-style fuel system (otherwise I wouldn't be running the Walbro, folks !)

The Walbro pump has been getting progressively louder since I originally fired the engine. At first, it was barely louder than stock. Now (and since the problem manifested itself) it's clearly audible from the cabin, and quite loud from outside the car. Keyser may be onto something...

Looks like I'm dropping the tank again...

Dan G. and his Cougar Forged internal (Diamond & Pauter) full 3L, "Monster" Kinger F/I cut & P&P, T3/4 60 trim .82A/R ADC turbo, SPEC Stage 3, Torsen, Greddy Profec-B SPEC II, Apex'i Timer, Lots of Gauges! Used to have: 3.0L SVT hybrid