fireman3758

Symptom is on a 99 Cherokee with 200k miles, the I6 and an automatic transmission.
I was driving down the interstate the other morning leaving work and after about 15 minutes a loud thud got my attention. It sounded like I ran over a pot hole, but there wasn't one and there was nothing felt in the vehicle, just the sound. I continued driving and after about a minute the it happened again, then again. It was not regular as in a tire coming apart or anything like that.
The transmission fluid was changed the week prior when I had to replace the pan gasket and nothing was out of the ordinary with the fluid. Replaced the valve cover gaskets that were leaking and did an oil change while I had it down.
After I got home I checked the transmission fluid level which was fine, checked the u-bolts on the drive shafts, pulled the wheels off and made sure that none of the brake components had somehow come loose with nothing found.
I am at a loss and would prefer not to drive it until I can at least get some suggestions from the community on what else I could look at to determine the cause.

salad

Check leaf springs and control arm bushings. Is it cold where you are, as the suspension cycles and parts unfreeze you could have interesting noises.

smooth move

keep on truckin till it quits. much easier to find problem that way.

fireman3758

May just have to drive it to fix it as suggested. Talked to a friend of mine who is a mechanic and he was stumped. If it dies hopefully I can get a cell signal

mschi772

Were you in 4wd?

fireman3758

Was in 2wd, going 70 mph down the interstate. Wasn't terribly cold, about 25 degrees or so. Short trips around town the last few days didn't produce the noise either.

Larry's XJ

Has it done it since the first 3-4 times?