on the 91 ef wagon awd, i have a rear diff problem. i assume its the diff for now unless other wise. as i accelerate while shifting into gear i hear a thump. it happens mostly in 1st and 2nd gear. i dont hear it in any other gear, i normally dont accelerate hard enough in the other gears. i replaced the main rear diff bushing but it is still there. i also just replaced the diff fluid too. nothing else has been replaced. all original parts for now. can anyone tell me what this thump is??

 

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