Hey guys, My wife's 2007 Suburban LTZ with 250K miles on it has a random hard thump/clunk when cruising down the road. I can't tell for the life of me where it is coming form and it seems to be very random. A bump seems to make it thump, but not all the time and it does seems to thump without a bump. It seems to do it less in Auto AWD and still less in 4 wheel drive and not at all in 4LO. Going around the block it thumped 13 times in 2WD, 2 time in Auto, 1once in 4HI on hard acceleration, and none in 4LO. Sometimes its very violent and you can feel it in the whole car and it jerks a bit, other times its a soft clunk. The clunk seems like it's coming from the front passenger side sometimes other times from the middle and other times seems to be in the rear. I greased the main drive shaft spline about a month and a half prior to the new clunking. I had a bad drivers side motor mount I just changed. I changed the transfer case oil, it was dark and a little thick. I attached a go pro underneath but still couldn't determine where the clucking was coming from, nor did I see anything happening to cause it. I've gone around in circles on what it I think it is for about a month now. I'm sure it is the transfer case one day, them I'm on to its the front diff another day. I really don't know what to do. I think my next steps are going to be changing the front diff fluid and all u joints. I was thinking of taking the front drive shaft out and see if it goes away, if it does I would assume Transfer case, if it doesn't I don't think it helps my diagnosis at all. Another thought was the Auto AWD clutches might be slipping or grabbing while in 2WD to cause it, which is why I changed the fluid. But wondering if I take the front drive shaft off and set up my go pro to watch the front output on the transfer case and if it moves during a clunk that would affirm my clutch suspicion. Otherwise I am lost, Anything you guys can think of to try or maybe have experienced this. I've searched the interwebs up and down and no one describes my clunk. I've talked to a couple car guys and a shop and they can't seem to point me in a good direction. Any help here would be much appreciated. Thanks in Advanced.

ohh, just saw I can upload attachments, I'm going to try uploading a video or two. I just took this vid as my last thoughts were the noise was coming from the rear. It for sure seems the loudest back here on camera. What do you guys think?

Nevermind, It was too big to upload so I made a youtube:

 

1st clunk at 1:24 in the YouTube video

 

On a side note, I also replaced the rear stabilizer bushings about a month before the clunking started. Could they maybe on to tight, or maybe the bushings are too "sticky" and the bar is getting caught up and popping loose? I don't know grasping at straws here, but then why would it stop when in 4 wheel or lessen in Auto.

 

Because the noise seems to occur when hitting bumps, it’s most likely a suspension noise. Removing the front driveshaft may change the sound but that’s not necessarily indicative of driveline concerns.

Despite being random, does the noise seem to be more frequent when first starting to drive for the day or after it’s been driven for a while?

Have you tried driving on gravel or non-paved surface to see if it increases the frequency of the noise?

Are you feeling any vibrations when driving uphill or even slight inclines?

Are you hearing any grinding or humming noises as well?