I have a 2005 ML500 141,000 miles, and I have had sporadic issues with a "thumping" noise that sounds like a flat tire and it is a very violent noise like a blown tire that is shredded. I have experienced this noise five times in about six months of ownership and the noise is not consistent or able to duplicate.These are the times I have heard the noise:

-45MPH 1/4 mile after sitting at a stop light. Pulled over, checked for a flat tire, nothing. Backed up, zero noise, headed home without an issue for around two miles. Thumping noise again, decelerating from 45 to 35, I was not braking. Pull over again, check for debris I may have run over, nothing. Drive home three miles and no issues for 1,000 miles or more.

-Driving 70-80mph on turnpike for 15 miles. no issues, decelerating on off ramp and thumping noise. Continues for 1/4 mile until I pay toll. Pull over and check again, nothing. Drive home on turnpike, nothing.

-Vehicle in park in driveway, won't move like parking brake is on. Shift into drive, reverse, neutral, won't move. Press and release parking brake three times. Moves like nothing happened. (could've pressed parking brake accidentally)

-After driving 25 miles 45-55mph leave store, go to ATM. Put vehicle in park while getting cash, pull forward and there is a "clunk" then thumping noise that hits on specific revolutions but cannot determine anything is wrong. Put in park, press and release parking brake (I was thinking parking brake was failing) shift into drive, still thumping. I have a passenger with me and he is walking with the vehicle, can 99% identify the sound is coming from the rear passenger tire area. Drive roughly 3/4 mile at several lights and when the thumping begins the passenger hears a "spinning" noise that he described as a vehicle with locking hubs 4x4 that was shifted into 4x4 without locking the hubs. Pull over, decide to get to passengers house approximately 10 miles away and no more noise.

-Driving 12 miles to work, stop and go traffic 35-55MPH, nothing. Headed home and hear one "thump" stopping at a light. Leave light and nothing for 1/2 mile then descending down a hill "thumping". Pull over, shift into park, try the parking brake trick. Nothing since for approximately 30 miles.

When this happens there is no pulling to one side. I don't feel any rumbling or rough ride. The ride is as smooth as ever even with the noise. I have also driven 60 miles round trip at 65-70MPH all highway driving without an issue and maybe a fifteen minute pause before turning around and coming home after making a delivery. I have driven 70-80MPH on the turnpike every Monday since I have had the vehicle and only one time I experienced the noise. I have tried to duplicate the noise and cannot recreate the noise. Since Friday when the last instance happened I have pulled the caliper and pads off the rear passenger tire. Cleaned a good deal of brake dust that had the rear pad stuck pretty hard in the caliper. Checked the CV axle and flexible brake hose for issues where hose creates an internal check valve from crushing and the brakes are good. I have a log of all regular maintenance, new tires, fluids good, rear differential fluid is good. The only other issue is in cold weather (not much of that lately in Ohio) is below 40 degrees there is a squealing on start up that goes away after warming up, most likely the power steering pump going but I always let a vehicle warm up five minutes and the noise is gone within 30 seconds, again the squealing is only when it's cold but I thought it might be worth noting just in case. I'm at a loss.

Thoughts?

 

You parking brake shoes have become disengaged. I would not drive on hway. at any high speed.

 

 

 

What is all that fluid on the drum and shoes?