I have a funny noise under the front of the jeep that is eluding me. It isn't consistent but it is getting worse. It only occurs when i'm travelling at highway speeds and when i am off the throttle (step on the gas...nothing...off the gas and there it is). If i'm coasting down a hill and the noise is audible I can put it into neutral and the sound will continue but if I touch the gas it will stop...so you'd think motor but if you hit a bump the pitch will change so it sounds and feels like running gear somewhere. I've pulled the tires checked the brakes...nope. Hub assemblies...I gave the wheels a good twist and nothing, gave the brake disks a good twist and there is no movement...they look good. The U-joints look ok too...I don't know what bad ones look like but grabbing, twisting, and turning them didn't show any slop. Just replaced the cooling system...thought it might be the pump(leaking...turned out to be the rad(cheap rad...only lasted two years)). No leaks in the trans case, or rear.
I'm thinking I'll go back to the hubs again for a closer look. Just had it E-tested...runs like a new jeep. It's a 98 cherokee ltd.
I have taken it in a couple of times...didn't make a sound for them. But, it is getting so bad you can feel it in the cab.

any thoughts?

 

The items I would look at are the front u-joints,also motor mounts and trany mount,if the are getting wore you will feel motor and trany vibrations more.
It can also be front or rear driveline u-joints.