I have read up quite a bit on this whistle that the 4.0 liter SOHC engine makes while accelerating. Sounds like something in the TB or intake to me. There are no definitive answers to the whistle that I could find. Has anyone resolved this whistling noise? It's a very high pitched whistle only while accelerating at about 1/3 throttle.

 

A whistling noise is sometimes indicative of a vacuum leak. Might not hurt to check the hoses.

 

It's not a vacuum leak, I've checked very well. There are tons of posts about this online on various sites. So far nobody seems to have pin pointed it. Almost sounds like air going over the butterfly valve in the TB. It's just enough to get annoying sometimes.

 

I have cleared this whistle on several engines by just cleaning the Throttle plate and body (TB cleaner and toothbrush). Seems air turbulence over dirt may be the cause... Philip

 

I will have to give it a try, Thanks.