Odd clicking noise after trans rebuild by dealer

Well its been about 3 weeks since I had my trans rebuilt under warranty at 48000 miles. Two days ago I noticed a odd/weird clicking noise when coming to a stop from neighborhood speeds and right before it down shifted into 1st felt truck lurch and rpms lowered and raised then made a sound that reminded me of an old truck dieseling but faster. Kinda like take a 1/2 ratchet and turning it. It only lasted a second or two. I drove back around the block to see if i could get it to do it again and I was able to get the sound again. I'm not sure if it is even a trans issue but since it was just done I almost have to point my finger that direction. If anyone has ever had this or could point me the right direction I would appreciate it. I am going to crawl under and just look around checking for loose stuff shop may have left heat shields and what not.

2208 x cab z71 5.3 4l60