2013 4X2 3.7 auto transmission 14500 miles.

I have noticed a smooth type squeal coming from my truck lately. At first I thought it was another car in traffic with worn brakes but noticed it was following me around! It is not very loud but it is noticeable in normal traffic with the window down.
Since I have been paying attention, it only happens between 1650-2000 RPM with normal acceleration and quits after 4th gear. I have no idea if it is in fact something with the transmission but it is tied to RPM and specific gears. As I said earlier, it is not loud but just loud enough to make you notice. I am taking it back to dealer as it is still under warranty but wanted to get some education before I take it in. Thanks.