started this past week. took the wife to dinner tonight. came out,started the truck,exiting the parking lot at a slow speed and clunk-seems to come from under the rear seat area . went to lowes, came out-drove through their lot,slowly-nothing. seems to do it once in the a while. came home-checked my u-joints (which were replaced a year ago with spicer greasables-seem fine) check diff fluid-fine. check my shocks (bilsteins with 25,000 miles on them-seem fine) checked over my front end (everything new-two months ago- i mean everything) everything seems tight. new brakes 10,000 miles ago. checked the exhaust system over-also seems fine. i can not find anything! i have no driveabliity issues-no vibrations-nothing. this clunk just started this past week! only will do it when i drive away from a dead stop, at slow speeds after the truck has been parked! also checked the tranny fluid-bright red (had it flushed two months ago) i am stumped! any ideas??

 

is the noise outside the truck or inside? it sounds like you've checked a bunch of stuff. it may sound silly but is the spare tire loose???

 

clunking noise is outside of truck. good suggestion about the spare tire! but it is secure. i checked everything externally. i don't know where to go next!!!.
i do have one more question, though- how much slack should there be when moving/rotating the drive shaft? i have about 1/4 of an inch.

 

update- noise is definitely coming from the front end (i thought it was the rear end last night) i drove to church, the grocery store,etc today- same scenario. trucks sits for a half an hour or so, get in and clunk within 20 feet of leaving the parking space!! entire front new!! except for sway bar end links,control arms and steering shaft. i have all new ball joints tie rods, poly bushing, trac bar,dss bar, lock out hubs and new axle u-joints-all done three months ago. check the steering box today-it is tight against the frame. steering shaft has a little play in it- i do not know if that is normal or not?? any ideas???

 

Mine was doing that, clunk shortly after it started moving. Didn't do it all the time. Turned out to be the front wheel bearing assembly.

 

can not be my wheel bearing assembly- i have brand new dyna-trac lock out hubs!!!

 

ok- update (i guess ) able to drive the truck more today- samething- truck needs to site. get in and drive- thump! (not a clunk noise) seems to be coming from underneath the go pedal and brake pedal. which makes me think steering shaft- but i checked it from on top (reaching in through the engine and the bottom-crawling underneath truck- it does not seem to have any play! the thump noise can come if the truck is going straight or the wheel slightly turned. does it once- then it does not do it again-until truck sits awhile, then i start her up and drive away!

 

Let me throw this out there… So it thumps shortly after you start moving... not when idling? I suggest take a closer look at the tranny. Perhaps a part is worn that causes pressure to build up slower than normal and when it does you get... oh perhaps.. a thump (slow/hard shift). I'm not sure off hand what servos are working and engaging gears at start off, but it sure sounds like one of them has become slower actuating or engaging with a thump. It could be doing it all the time, but you only notice it when moving slowly. I know just enough to be dangerous here, but both my dakota and jeep transmissions have done weird things.

Is the transfer case locking/unlocking on it own...

Otherwise is there a component that runs for a few seconds after you start, and, when it turns off, it now thumps?

Checked the tranny fluid level right?

 

Not sure if I have the same noise as you, but My new 07 5.9 will do that on occasion as well and I have the 6speed. Sounds like the AC door or something closing, opening, etc. Doesn't bother me though so I am not sure if it's even the same noise as yours. Usually happens a few feet after driving... Since there were no issues I have never worried about it, mine did it the day it was new driving off the lot...

 

Mine does that as well, but only when the a/c is on. Try to have the a/c off and see if this still happens. It is a loud thump or clunk. It concerned me as well but seems alot of people have the same symptoms to no ill effect.

 

I have the same noise from the air conditioner. It kind of clunk noise as if someone has smaked the underbody with a sledge. I guess it must be the compressor engageing?