Based on your description, it sounds like one of the pins in the differential have come loose and are hitting the trans housing. THis isn't uncommon. However, if I am correct, you could crack the case and then you will end up with additional problems.
If you look behind the trans, the differential housing is part of the trans housing. You need to remove the cover and gear lube to check it. Inside there is a pinion gear and in the center, spider gears held together with steel pins. Make sure nothing is coming apart.
Joe
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Wednesday, March 3rd, 2010 AT 1:37 PM