2014 Sorento LX 2.4, FWD, auto trans., 95,000 km
The trans makes a single thump when first driven on cold days. It is fine for the rest of the day.
If you are the original owner, the car is still under warranty. In any event, take it to the dealer and have the fluid level checked and maybe changed.
How do you know that the noise is coming from the transmission itself?
This could be a symptom of bad motor mounts or bad transmission mounts.
In any event, as Mustangman noted–if the 10 year/100k mile Powertrain Warranty is still in effect, you need to take the vehicle to the dealership for diagnosis and repair of a possible transmission problem.
By my calculations, 95,000 km equals ~59k miles, so the Powertrain Warranty should still be in effect if you are the first owner. If you are not the first owner, that warranty will expire in less than 1,000 miles, so you need to take it to the dealership right away.