Originally Posted by madfire
My 98 did that when I put in a new motor. If it sounds like an oversized tea kettle check your manifold bolts. One of mine needed tightening and the sound went away.
There have been a few other threads on here about that annoying whistle in the later models. My wifes 01 does it when I let off the throttle. Several others have had the same thing and a few of them have dured the problem by replacing the intake/exhaust maniflod gasket. They will develop a small leak as they age and the whistle is caused by air being sucked in through the gasket.
First check all the manifold bolts to make sure they are torqued to specs. Don't just slap a socket on them and start cranking down on them either. That will only caused more problems by splitting the gasket from to much pressure or break a bolt off in the head.