Front End Chatter when braking only in 2WD; not brake related

[titan7373]

Ok, got a good one. I have a 2005 2500 Duramax 4X4 with 157000 miles. I am getting a chattering noise when I slow down under moderate brake pressure only when in 2WD and after the vehicle has heated up. I can not reproduce the noise when it is cold or when I am in 4WD. noise sounds like the front brake caliper hanging up and releasing, however I inspected all the brake components and everything is in great shape. the U joints on the front drive shaft are also in good shape and I could not detect any slop in the axels and wheel bearings. the vehicle does not make any other driveline noise until I am braking.

[titan7373]

ok, in the chance someone reads the first question. I found what was making the noise. it is the rear section of the upper rear drive shaft that is coming into contact with the center support bearing. the bearing is new and installed correctly so I am not sure why I am getting movement there when I brake. I am going to check the slip yoke and see if it is seized today. it is potentially pulling the drive shaft back as the truck noses down when breaking.