Weird squeak'ish type sound coming from intake manifold

[Soledad]

I bought this truck about a month ago and ever since then I've been trying to learn it's quirks and nuances all the while doing all of the PM on it that it so desperately needs.

On Tuesday I had to replace the degas bottle and radiator as both of them sprung a leak. After I got those replaced and was burping the system I was revving up the engine a little to heat it up a bit quicker. I noticed that every time I returned the throttle to normal there would be this weird low pitched squeak sound coming from the intake manifold. It happens about .5 second after the throttle plate is closed.

I thought it was the throttle body but nope. And I thought it might be the IAC but it's not that either. I put my ear on the intake manifold and sure enough it's coming from in there. Thinking it might be the IMRC I disconnected the vacuum hose and then rev'd it up again and didn't hear the sound. I then reconnected the vacuum hose and could never get the low pitched squeak to come back.

Has anyone else heard the Intake Manifold Runner Control flappy things make this sound? Is it normal? I think I'll try to get a video of it today during lunch if I can.

 

[Soledad]

Ok, finally got a video:

https://youtu.be/GpG5NQc_U_8

Does any body else's make that sound? Is it normal?

 

[Soledad]

UPDATE: I found the source of the problem.

The IMRC actuator was disconnected from the intake runner flaps rod. And so when I was revving up the engine it must have been sucking them closed or open (not sure which direction). I reattached the actuator arm and no more sound AND the truck drives great now. It doesn't even buck any more.

But now I have the IMRC tick. Looks like a new intake is in my near future.