Dealer replaced differential today
'05 owners....I had the diffential whine issue. Picked the car up today after dealer replaced the differential. The whine is greatly reduced. There is still a very faint whine 40-50mph under light decelleration. Also the back lash seems to be reduced. I am pleased with the replacement differential, most would not even notice any noise, I think I am probably just super sensitive to any rearend noise due to having the whine issue and diff. replacement.
If you have noticable rearend whine you can take your car to the dealer, Pontiac has a program to correct the problem...they replace the entire Differential assembly. If the problem exists it will likely happen at 40-50mph under light acceleration and/or deceleration.
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