The IAC, when opened up by the PCM, can cause such a noise as you describe. This would be very easy to hear if you have little or no induction system installed.
But this noise you are hearing may just be the result of some other issue (causing the PCM to open up the IAC) and it may not be the cause of the problem. It would be helpful to see what the scan data is showing when it starts running bad. Specifically, I would like to see the following data:
-RPM
-IAC position counts
-o2 sensor voltage (B1S1)
-Short Term Fuel Trim %
-Long Term Fuel Trim %
-Spark Advance deg
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OVERKILL IS UNDERRATED
Custom GM OBD1 & OBD2 Tuning | Engine Conversions & more | www.gmtuners.com[This message has been edited by Darth Fiero (edited 04-20-2015).]