Probably need to add some rear end friction modifier if you have a limited slip rear end.
My 97 did that and I thought I was going to have to rebuild the rear end till someone on here have me the same tip.
Added a tube of friction modifier and everything settled down and the clunking stopped.
I used some from Oreileys auto parts and it worked just fine. After I added it I read where it was highly recommended to use ford specific friction modifier.
You may hear this stuff called 'rear end dope' as well.
I would change the rear axle fluid and add friction modifier to it.
Good luck, Jeremiah
