Weird noise, sort of sounds like a soft whistle.

Hi every one, I'm new to this forum and Tacoma's, but my truck recently started to make a funny noise and I have no idea what it is. At about 15-30 mph I'll hear a weird low whistle/howl sounding sort of like "wum, wum, wum, wum" it's very very soft and only happens in that speed range when it is 60°f or warmer outside.
Sorry if it is an over asked question, I just can't seem to find the answer. Any help is appreciated and welcomed, as this noise is freaking me out because we're about to take the truck on a long road trip.
So you all know it is a stock 2015 Tacoma sr5. Only thing done is after market wheels and tires. 265/70-17 duratracs and 17" wheels.