98 4x4 5.2 i have noise coming from under truck while driving over 30 mph, like a growling sound disappears when i just touch the gas, but if i turn off engine the noise is still there while coasting also. The other day transfer case got stuck and when it went back into rear drive the was a big noise, but didnt hear growling till a few days later. replaced rear u joints, and breaks are fine. any one have a clue.

The catalytic converter is plugging.

you say maybe the catalidic,, but it makes the nise also when i turn engine off and coast in neutral also,, so i dont think it could be,, maybe from u joint on front axle???????

Maybe it's coming from the transfer case or something?

i just had it in 4 wheel just tonight,, and the noise was not as loud,, i did snap a ujoint on front passenger side last year and they said there was a little play in it because i drove on it after it snapped,, what would make the noise in transfer case,, thanks

I guess something is vibrating? If there's play in it, it might be moving back and forth real fast...

Seems like if there's almost any unnecessary movement in the driveline, it will chug and growl and vibrate...

well we got 10 inches of snow here, plowed snow for almost 30 hours and nothing broke on truck....seemed couldnt hear noise when under side of truck was packed with snow,, but its back...aleast i didnt break down... still dont know where noise is coming from

I had the same problem with my truck. I suspected the rear end. so i took it to the dealer to have it investigated. they told me that some packing material came loose and got into all of the bearing and the trac-loc. They were going to charge me 700.00 for just the inspection and 2500.00 to repair the problem. I told them no thanks and went to Pro-Gear in san diego they fixed it better for only 500.00. I hope this helps I suggest go to a local repair shop you trust instead of the dealer.

Packing material???? what would that be ,, are saying it got into gears in rear end???? maybe i can fix myself...let me kniow excatly what you think got into gears,, and if it is some material in there,, wont it wear out its self,,, thanks for the reply

I don't know what material it was. I had it done over a year ago. Simple thing to to is drain the pumkin and remove the inspection plate to see if any foreign material is in there. I did not get to see the material because of the problems i was having with the dealer. You may be able to fix it your self I did not have the time.

98 4x4 5.2 i have noise coming from under truck while driving over 30 mph, like a growling sound disappears when i just touch the gas, but if i turn off engine the noise is still there while coasting also. The other day transfer case got stuck and when it went back into rear drive the was a big noise, but didnt hear growling till a few days later. replaced rear u joints, and breaks are fine. any one have a clue.
you know what, I have the exact same problem.....I checked everything and I'm just running out of ideas 2!!! Tranny fluid and filter changed, transfer case, u-joints, rear end was done a year ago, and now I have this noise I've never heard before. it's exactl how you described it!! In my truck you can't hear it until you reach about 100km/h. the noise is high pitch!! As you slow down, the noise comes back and comes on strond at about 50km/h and fades away completely at a crawl. Please let me know if you find anything out about this I would really like to fix this problem. Thanks. Have you change all your fluids??? That's about all I can say for now, If I find a cure for this Problem I'll will for sure keep you posted!!