Bumping noise from rear while driving

I have a 97 Explorer that has a bumping while driving at highway speeds. Ithappens at all speeds when the vehicle is not under heavy load just cruising. It feels like a skip except for the clunking noise. One mechanic says it's the differential one says transfer case. Any Ideas??

check your universal joints... you might wanna change your rear differential fluid also.. you could have a bad axel in the rear. is the bump on one side of the vehicle or both sides. if its one side you might want some one to fallow u to see if you can see the wheel wobling if it is most likely you have a bad axel. i had a jeep do the same thing a new axel was about 900$ but u can get one from a junk yard. oh and the axel isnt the whole differenial its the peace that slids in to the differential that the wheels attached to.

I have the same noise in oure 1996 explorer it sounds like the spare tire is loose but I checked that and Im still looking for the sorce of the noise will get back if I find it .

My 97 does it too. I have replaced fluid in rear diff and trans case, still doing it. It almost sounds like a u joint, I will prob. start replacing them this weekend. I will let you know the outcome.

Take the dead body out, i have found that on long trips to the country you will notice this sound, once you take out the shovel and dead body the return trip is all the more pleasent.