I had this problem. I asked several good mechanics for a diagnosis and got nothing that helped. Some people (on Internet sites) describe it as if someone slightly bumped your vehicle from the rear with their vehicle. It drives you crazy wondering what will come apart from the apparent abuse of this symptom. Finally, I read that lubricating the slip yoke on the rear drive shaft (on two wheel drive vehicles) would remove the noise and feeling at least temporarily. The advice quoted from GM was "don't grease 4X4 slip yokes because it will pollute the transfer case lubricant causing more problems". The solution for 4X4 Yukons/Tahoes is the replacement of the slip yoke with a nickle plated slip yoke. My mechanic snickered when I presented him with a nickle plated slip yoke, new shaft seal and u-joint, saying that I shouldn't come back complaining that the noise and feeling didn't go away. Well....as others have said: "the problem is gone after the new parts were installed". I got the nickle plated slip yoke from Fort Wayne Clutch and drive line Co. for about 1/2 of what NAPA quoted for a plain steel slip yoke. It comes with the universal joint for the yoke.
Fort Wayne Clutch & Driveline 32 SPLINE NICKEL PLATED TRANSFER CASE SLIP YOKE, TH400, 4L80E 32 SPLINE NICKEL PLATED TRANSMISSION SLIP YOKE - 7 7/8" LONG - PN#(S) 88963576, 40032054, 12479383, GM TSB #01-04-17-004B

 

my 2008 silverado was doing the same and all i had to do is slide the yoke out put some grease in it and that fix the problem. but yeah make sure you choke your wheels if you pull the drive shaft out