Dies while idling, LOUD humming noise between 1k-2k RPM

My wife bought a 2000 GT and everything was great until... we went on vacation for a week and when we got back it started making a loud humming noise when you'd start the car up ... all the way up into about 1.9-2k RPM.

I have

Cleaned the MAF (didn't appear to be dirty)
Replaced a bunch of tubing that was cracked and soft
Cleaned the IAC (or at least I thought I did)
used some throttlebody cleaner on the intake with a toothbrush

There is no check engine light... took it to oreillys and there were no codes.

I have not

Replaced the IAC
Looked at the intake manifold (not even sure what to look for here)

I have noticed that if I take off the baffle that connects to the IAC (this one: Little black box. What is this part?? - Modular Depot Forums) that the whining appears to go away.

Any other advice?

I actually have replaced the PCV valve.

Will look over the link you posted. Thanks!

All Fixed

Went to Autozone and pulled the electrical connection off the IAC.... nothing changed. So I bought and replaced the IAC with the $52 option from autozone... so far the noise is completely gone and I haven't had die on my while idling since. Thanks wmburns!