What does this part do?

[trebuchet03]

My intake temps fluctuate pretty quickly... If I'm moving with a mostly closed throttle, IAT goes up. If I open the throttle and allow the rpms to climb, IAT goes down. If I'm coming from a stopped idle up to speed, my intake temp can drop 15+ degrees while accelerating and then climb back up a little bit when I steady off my speed.

I'm fairly confident it's just a function of mass flow, heat soak and the intake source. At least in my case

I also don't notice any sound increase without it. I'll report any significant FE changes as well.

Unless you've got flappers in there to change the intake length -- that resonator is optimized for one specific frequency. Likely the loudest one... You probably won't notice it until the right conditions - or you'll pass it so quickly it won't be very noticeable...