Recently changed the rear brakes. Since then, I have noticed that when the truck is cold, I get a distinct "thump" in the drivetrain on takeoff. It doesn't matter if I take off slow or hard, it is still there. I can feel it in the seat and in the 4x4 shifter. It only lasts for a second and then is gone. After the truck warms up, the thump is gone but is replaced by a low pitched whine/groan that again lasts for just a few revolutions of the tires and then is gone. No other apparent tranny/diff problems. No whining. No slipping. No grinding. It only happens when taking off from a stop.

Any ideas?

2005 5.7 QC 4x4 w/ LSD and 3.92 gears