1999 Chevy Suburban clunk coming from the rear when I accelerate

1999 Chevy Suburban K1500 LT 5.7L 4x4 66,000miles. I recently purchased this Suburban and probably half the time when coming to a complete stop and then accelerate there is a clunk sound coming from the rear of the vehicle. It's just one klunk and then everything is fine until I come to another stop. I suspected a bad u joint and had the mechanic at the Chevy dealer check it and he said it was in good shape and that the sound I'm hearing is normal for Suburban's and Tahoe's as the rear end is synchronizing with the transfer case. I have several friends with similar Suburban's and have never heard this sound when riding with them but they certainly hear it when riding with me. I just got back from a 1,700 mile trip and several times the klunk sound was much louder and one time it klunked so loud and hard I thought I may have a transmission laying on the ground. Always after the initial klunk it drives just fine. A friend of mine said it sounds like a bad yoke. Is replacing the yoke an expensive procedure? Any ideas?