Strange Sound from Transmission

So I have been towing with my Tac this year, got a 23' travel trailer comes in around 4600lbs loaded. Well within the rated capacity of the truck. In the last couple of days I have been hearing little bit of a knock and whine when shifting from P to D and back to R. All is well once moving though.

Only seems to be happening when cold.

The truck is an auto but I shift manually quite a bit when pulling, it only has 37500miles on it. As I understand this is early for a transmission service.

Any thoughts? Could it be the pulling that has induced early wear? The manual shifting?

I plan on taking it in to the dealership next week but have a trip planned this weekend, should be safe right?

 

First gen guy here so maybe a dumb question but can you check your auto trans fluid for level.color, and smell or is your's one of the sealed transmissions?