So I have a 2001 4.0L and it's developed this weird whistle noise when turning on at idle and it may continue while driving but then it will go away. It honestly sounds like a vacuum leak but I can't pinpoint it. I've recently changed gaskets ( valve body gaskets , and valve covers are in good shape. And intake manifold gaskets.where else should I look ?

 

I've taken the liberty of uploading a video of the whistle on my Google drive .... https://drive.google.com/file/d/0B2Q...p=docslist_api

 

Fuel trims (LTFTs) will tell you if it's an air leak. (Then if it is you can spray tiny amounts of burnable gas and the STFTs go mad.)