Definately sounds like a warranty job to me... Either they have put the sub in an enclosure that's too large for it, and it's bottoming out, or there's a defect in the sub...
I treat my 13TW5's with utter abuse, and they have to put up with more power than your 13TW5 is having to contend with at the moment. Something may have not been setup properly (maybe), but the 7" voice coils on those things can handle some serious voltage, as long as the box is kept under 1cuft. Over 1 cuft, and the sub might be bottoming out IMPO...
I treat my 13TW5's with utter abuse, and they have to put up with more power than your 13TW5 is having to contend with at the moment. Something may have not been setup properly (maybe), but the 7" voice coils on those things can handle some serious voltage, as long as the box is kept under 1cuft. Over 1 cuft, and the sub might be bottoming out IMPO...
