Hi, My Jeep with a 4.0 Has the same whistle, But today I waited until the whistling started, Then I put a 15mm socket with 1/2" Drive on the very back top mounting bolt of my intake manifold and tighten and the whistle stopped, I have been on the road all day and it has not whistled at all. But now I can hear that I need to check my brakes they have a squeak that I couldn't hear over the whistling.
Now it may not be the last bolt on yours, it could be any of them or even all. Also torque setting for those bolts is 24 ft-lbs, I took it to 35 Ft-lbs on a hot Engine, and hopping it will be okay. If you don't have a Torque Wrench then just tighten until the whistle stops or bolt brakes.
You may need to replace manifold Gasket, $9-20 call around. But tighten the bolts will tell you if that is what is making the whistle.
Thursday, March 20th, 2008 AT 5:06 PM