Need help diagnosing the cause of this sound (2004 GT 4.6 Manual)

Hello guys I’m new to all of this this is really my first car so any help is appreciated, so there’s this unusual noise coming from the passenger side kind of in the engine bay it only happens when coming to a stop, sometimes it will happens when just idling or when the car is turning off, it goes away whenever I rev the car and it never happens while the car moving. It’s doesn’t happen every time but it will it do it ever so often. Again any help is appreciated Here’s a video of the sound https://imgur.io/a/Q4oPq4M#80C4E5n

Yea the car would vibrate a little bit, it goes away if I rev it up but if the rpm’s drop back down to normal the sound will come back. it happens every now and then, so I’m not really sure what it could be. The car has sat for a while if that helps I think around 3-4 years

PSKSAM2 said:

That is an odd one, almost sounds like a Jake brake. By the sound I would have guessed brake or suspension related, but it doesn't seem to correlate with the car's speed in the video, and you said it can happen at idle or when shutting down. Can you feel any vibration when it occurs?

Maybe belt or pulley related?

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