Backlash noise

I purchased a 2002 LS 1500 4-wheel drive suburban on Dec-26 and it's been in the shop more than it's been at my house. My question for you sharp chevy guys is as follows: Is it normal to get a clunk sound when shifting from park to drive or from drive to reverse on the 2002 4-wheel drive surburban (Mostly when it warms up). I have taken this car to three seperate dealerships and they have all said the noise is normal backlash. The problem is I have a 12 year old car which I drive hard and it doesn't make noise. I've tried lubing the trans imput shaft, Dealer says U-jounts are good. Someone says transfer case fluid might need to be changed but it only has 21000 miles on it. Please Help.