All,
I open my hood in the garage to let out the hot air when I pull in after work.

Heard a buzzing noise.

Put my hand on the idle air control motor..
Was vibrating with the engine off.
Key off.

This seems like a problem which will eventually ruin the idle control motor mechanism.

 

Pull fuse 1 in underhood box. That runs a lot of engine management including injectors and the IACV. If pulling that kills the "buzz" maybe the main relay is fried.

 

Also can be worn ignition switch

 

This is interesting as we are running into the same issue with the IACV. The other thing we noticed is the fuse block under the hood has a clicking noise from one of the relays and we tracked it down to the ABS relay and pulled that relay and no more clicking. When we pulled the relay for the ABS we heard an under lying sound that sounds like a faint buzzing soundcoming from the fuse block. coulkd this be realted to the IACV making its buzzing sound?

 

Probably.
I do appreciate the feedback.
Great detective work.

All I know - is
'systems still on'
with key off - are trouble.

Either will drain the batter and / or will destroy the part in question.

I need to do more troubleshooting.