I think its the ujoint..i finally got under it again when i did my starter, and i get quite a bit of movement from the joint..so looks like this weekend i get to pull the y pipe and trans x member and replace the ujoint on the tcase side...

and tips to replaceing a ujoint? never done it before

 

I was gonna say check your sway bar bushings/end links

 

i had a bad front u joint..replaced it today..all is well...but damn i hjate pulling the LPP y pipe and **** off..gotta drop the trans x member and all the clamps. then try to get it back in place perfect lol...

 

well the u joint didnt fix the problem...i have no idea what the clunking is..been doing it for 2000 miles...in the spring im redoing the suspension(tie rods, control arms, shocks, idler/pitman, balljoints etc) so i guess if that doesnt take care of it then im not sure what will..I plan on redoing the brakes again with a nicer set up so if it was my brake pads/rotors, that should take care of it

 

That sucks.

And for some reason, mine stop clunking and the play I once felt in it is gone now. I dunno

 

ya its really ******* annoying, but theres not much i can do now that its below 0 and the entire underside of the truck is full of snow lol

 

Heres another Tsb I found on my '07 Tahoe, it looks like they have problems with the slip yoke, and the best bet would be to replace it. It doesn't list older models but I remember reading somewhere they could have problems too.

Im gonna order mine from gmpartsdirect.com the part number for mine is 19121437 I would give your local dealer a call and confirm the part number for your vehicle though.
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Drivetrain - Bump Feel/Clunk Noise at Stop/Launch


TECHNICAL

Bulletin No.: 09-04-17-002C

Date: June 15, 2010

Subject: Bump Feel/Clunk Noise at Stop or from Launch (Clean/Lubricate Propeller Shaft Slip Yoke Splines)

Models:
2007-2008 Chevrolet Avalanche, Suburban
2007-2009 Chevrolet Tahoe
2007-2010 Chevrolet Silverado (New Body Style) with Single-Piece Propshafts
2007-2008 GMC Yukon XL
2007-2009 GMC Yukon
2007-2010 GMC Sierra (New Body Style) with Single-Piece Propshafts
All Equipped with 4L60 Automatic Transmission (RPO M30) and 2WD

Attention:
This bulletin contains a procedure to clean/lubricate the slip yoke splines and replace the slip yoke, if necessary. Check the history on this vehicle. If the lubrication procedure has been performed previously, then continue on and replace the slip yoke.

Supercede:
This bulletin is being revised to add a U-joint part number. Please discard Corporate Bulletin Number 09-04-17-002B (Section 04 - Driveline/Axle).

Condition

Some customers may comment that the vehicle has a bump feel or a clunk noise at a stop or on launch. Customers may also comment that the bump feel or clunk is noticed after the vehicle has come to a complete stop and that it feels as if the vehicle was bumped from behind.

Cause

This condition may be caused by a slip/stick condition in the interface between the rear propshaft slip yoke and the transmission output shaft splines. Braking to a complete stop can force the propshaft slip yoke forward into the transmission while the vehicle rebounds slightly backward after stopping its momentum and create this condition.

Correction

Note
A bump feel or noise may also be due to fuel movement in the fuel tank when not completely full. If the condition is eliminated after filling the fuel tank, the noise is isolated to the fuel movement in the tank. Please make no repair attempts, as this noise is considered an operating characteristic.

Verify the customer's concern.

Clean/Lubricate Slip Yoke Splines

1. Remove the rear drive shaft. Refer to One-Piece Propeller Shaft Replacement in SI.
2. Inspect the rear slip yoke splines on the drive shaft.
3. Clean the slip yoke splines with brake cleaner or equivalent and a shop towel.
4. Assure the yoke is free of rust or other foreign material.
5. Lubricate the slip yoke spline with grease, P/N 19257121 (in Canada, 19257122), using a brush or swab to completely cover the entire spline with a light coating of grease.
6. Reinstall the rear drive shaft. Refer to One-Piece Propeller Shaft Replacement in SI.
7. Road test the vehicle and verify that the noise is gone.

Note
Do Not replace the slip yoke unless the cleaning and lubrication procedure is ineffective.

8. If the vehicle has a repeat concern after lubricating the slip yoke splines, it may be necessary to replace the propeller shaft slip yoke with a new nickel-plated slip yoke.


Replace the Propeller Shaft Slip Yoke

1. Remove the rear drive shaft. Refer to One-Piece Propeller Shaft Replacement in SI.

Important
Some U-joints are fastened with nylon injection clips. If so, Do Not reuse the U-joint. Replace with GM P/N 12479126 U-Joint kit.

2. Replace the propeller shaft slip yoke with a new nickel-plated slip yoke. Refer to Propeller Shaft Slip Yoke Replacement in SI.
3. Install the rear drive shaft. Refer to One-Piece Propeller Shaft Replacement in SI.

 

thanks for reminding me...that was the only thing i did not check as i thought it was coming from the brakes...ill check that out as soon as i can

 

Hey kinda new to the form. But I get the same noise!! I was thinking it was the u-joint. Not really sure, I started to notice it after I did the in stall on my trans. Been trying to look at it just not any time. Let me know wat you find out, thanks and good luck.

 

i did notice yesterday that it clunked when i didnt hit the brakes one time..i downshifted from d-3-2-1 and hit 1st going about 20 and it made the same clunk as if i hit the brakes..so im thinking more and more its the slip yoke since downshifting would act like braking on the slip yoke..ill hopefully get to mess with it in a few days and go from there