:hmm:At first I thought it was a u-joint. I replaced the driveshaft with one I knew was good, still rumbled. Put a rim and tire that I knew was balanced and straight on the right rear and then the left, still rumbled. So I think it is the rear end. I have a '85 Fleetwood with a good rear to swap. It has some kind of vibration damper on it. It kinda looks like a small piece of leaf spring with a canister like weight on the end and it is attached with shackles. Was this a factory option? The reason why I ask is because I'm wondering if there was a vibration/rumbling issue with the car that caused someone to put an aftermarket damper on the rear end. I also thought that maybe it was a factory option to enhance ride quality. Which of these assumptions is right. If neither, please tell me what is right. I don't want to swap the rears and still have an issue. :bonkers:Thank you for your input.