[Biturbos4] differential thump

[T Stifler]

Hello folks,
I have an 02 Tip - under initial hard acceleration (1st or 2nd gear) there
is firm thump sound and feeling coming from rear diff.  After one thump, it
seems to "seat" itself and I can not make it reoccur until 40-50 miles of
casual light driving (normally next day or so when I punch it).  If I ease
into it a few times, it will seem to be ok, w/no thump.  Could there be
something wearing out in the differential ? Any idea ?  I recall this
feeling a few times over past couple years, but it's becoming the norm now.

Merry Christmas, Happy Holidays everyone.
TS