Problem solved
Was getting a rumbling from the TC under heavy acceleration. Went to Ford and the shop manager (a real nice guy) diagnosed the problem right away. At no cost. Seems that the new tires I put on the front had a different profile than those on the rear (about 20000 miles on them by my estimate), even though they were the same profile (255/75R17).
Guy says 'you're not going to fix the rumbling/thumping by reflashing for tire size, and explains that a difference of as little as 1/8" in profile results in enough mismatch in RPMs to mess up the control equations for the A4WD. He says you have to replace all 4 tires at the same time, etc., of you're going to get this kind of a problem. I went back to the 16's (all 4 new). problem solved. Once I get enough $$ to buy 4 17's, I'll go back.
Oh, and by the way, I'd assume that tire pressure differential front to back, etc. might induce problems similar to this. Can you put a switch on teh magic brown wire?