Hoping somebody can help me diagnose this. Its a GM V8 6.0l with 95K miles. 2003 H2 Its making a sound like cats screaming. And before you ask, there is no cats, kittens or other furry animals in the engine bay. The sound seems to be coming from the Intake Manifold on the passenger side at the rear (opposite end from the throttle body.) The drive belt has been removed, so its not any of the front end accessories or pulleys. The engine idles and runs smooth. Its gotten worse, it used to just make the noise when you accelerated, we did some testing at idle revving the engine, and now it does it just idling. In Park, not moving it makes the squeal. Can a vacuum leak make this noise? I've heard that the plastic intake manifolds can develop gasket leaks? I was going to get a mechanics stethescope and look around. (Already tried the long screwdriver stehescope trick.) I'd appreciate any ideas.