4000q rear clunk

[Rich Walker]

Hi.

I'm in the market for an 85-87 4kq.  Two that I've driven recently have had an audible "clunk" coming from the rear differential area when letting the clutch out after shifting.  Both had around 130k miles.  One seller suggested the noise was caused by worn "rubber stoppers". Any suggestions on what the cause of this could be and possible expense of repair?
Thanks for your help

Rich Walker
Portland, OR