Howl/Moan Sound Issues?

Ive posted this before but it had stopped for last few months so I didnt worry with it.

Well now my issue is back.
I have howling/moaning sound coming from the air duct throttle body area. I can remove the entire air duct and the sound is actually coming from the throttle body. I have used some seafoam spray with little help to the issue.
It mostly does this when its cool outside and normally stops after warmup but not always. It only makes noise at 1000 rpm or at idle. Driving around its quiet. At idle it does it unless I just bump the gas, then it gets quiet until 1000 rpm or less.

I have a restrictor plate that goes between the IAC and where it mounts onto. If I install it it there is no sound but if I remove it well all the above. It was designed for the hanging throttle issue some Machs have. Mine doesnt have it and having it installed makes the idle drop too fast especially when cold out and makes for rough shifts so I dont use it.
Replaced IAC before and that did nothing.

Anyone have any idea whats going on?
Im lost here.

2004 Mach 1

wmburns said:

Is the square helmholtz resonator still in place between the air intake and the IAC?

What happens if you clean the inside of the IAC?

What about drilling out the hole in the IAC restrictor plate to the next larger size? Or adding additional very small holes?

Click to expand...

Not sure what "helmholtz resonator" is? Never heard that name before. As far as everything still in place its all original.
I removed the restrictor plate since I dont have the hanging throttle issue and when the motor is cold it makes the RPM's drop too fast and makes for sloppy shifts,probably more me than the plate.

I have cleaned the IAC and didnt seem to do anything at all.
Used the Seafoam throttle body cleaner also,not much a difference. The issue has only started in the last year,car has just under 100k miles on it.

I thought about making a bigger hole in the plate mentioned but since the piece is a one off from a member here a few years back, didnt figure it would be replaceable if I ever did need it. Sorry cant remember who it was that sent it too me now.
Guess I'll try that soon.
The noise Im sure is coming from the throttle body. Without all the duct work attached its even louder out of the throttle body.

With plate its mostly quiet, just when cold it makes a little moan sound. Without its awful on cool days.

Are you meaning the circled item in pic?
If so yes it has it but as I said above,doesnt matter if the duct work is on or not,still makes noise.

BTW, that pic isnt my car,I just grabbed it off google images

Forgot to mention.
Recently this piece here dried out and broke apart which made the sound go away, but since replacing the part it has made the sound come back.
Circled in yellow.

Well I may have fixed the issue....?
My PCV elbow was split and I changed it out yesterday morning. Car hasnt been moaning since, guess time will tell.
I sure hope its that simple,doubt it knowing my luck...lol

Update for anyone that might need it. ANytime Im troubleshooting and asking for help in posts, I like to follow up if and when I get it fixed.

The PCV elbow quietened it down but was still there.
So after looking over everything I could think of, even made a homemade smoke machine to track down any vacuum leaks of which there were none I figured I'd try something.

I removed the silencer( the snorkel of the air box into the fender) then I also removed the milk jug ( red circled item in above pic) and capped it off with a #9 rubber hole plug and a hose clamp. so far almost 2 weeks moan free. Crossing fingers it stays that way. Im just going to order a CAI soon since the main air duct is dry and small cracks, dont think its sucking air from what I could tell with a spray bottle of water and a few drops of Dawn.

Also while looking everything over closely I noticed my right motor mount is dry and separating so I'll be ordering those.