Regarding the idle control valve

Hmmmm. Generally speaking, the IAC doesn't squeal. They "moo". They fail because the pintle or valve inside is subjected to exhaust gas from the EGR and blow-by from the PCV system. They build up crud. It's possible that you have a vacuum leak though(collapsed and split PCV tube etc.) I do have to remark about aftermarket parts - many do not have the durability required for the real world. There are many sources for noise under the hood. A section of garden hose held to your ear while poking around the squealing engine will confirm its source. In the workplace, I have an amplified set of headphones called and "Engine Ear" with a microphone that can isolate engine sounds. Some use a stethoscope - cheaper.

"Moo" is a good description. Thanks for your help. We will check for vacuum leaks etc...or maybe a defective part.