Thanks everyone for all the good advice and info,
What I plan on doing which will hopefully buy me some time to figure this out and pin point who's side the trouble is on is to:
Step:1
Program up a DCS compact with the same configuration as they have now on the 7100 (5-28 button falcons & 4 COs) plug everything into the compact and see what happens, if the lines continue to flip out then I guess I'll know if it's on AT&T's side, unless of course Murphy's law will say that the compact's co card isn't as sensitive to higher line voltage as the 7100. (then I'm screwed)

Step 2:
Feed the 4 single line ports of the 7100 or compact back into the 4trm card of the 7100 with 1 28 B falcon as the answer point and again, see what happens (my gut says zilch) or I could tap off the AT&T lines to both switches at the same time. Any thoughts on that one? Or here's another one, program the 4 Single Lines's on the compact in with the operator group and then feed them into the 7100 as CO's??

Step 3: Overnight a 4trm and eat the cost, I should have a spare in stock anyway.

Step 4: if the customer is still not satisfied with my service after all of this, especially if it turns out to be an AT&T issue, I will give up and become a rodeo clown.

Mark (future buckeroo )