I don't want to step on OP's thread but I have the IAG onboard compressor kit installed as well.
The noise level is not insignificant, and it does pass a little bit of vibration through the rear door. I have a portable Viair compressor (450P I believe) as well and the noise levels are similar...
A bit late, but I saw your post the other day before ordering mine. Picked it up today, below are the numbers on that piece itself from the kit if helpful.
As everyone has said - it probably never gets as quiet as a fixed-roof vehicle. I did some sound deadening material in the doors and throughout the rear floor/sides and it made quite a difference - but also made the wind noise around the roof/seams stand out more.
The worst noise I've had was...
Awesome wheels. Not sure if you've had a chance to put many miles on them yet or not - pretty significant weight savings from OE especially if you had the factory bead lock capable wheels - any tangible feel to the reduced weight?