High Pitch Whistle at idle

I've got a 2001 and the thing likes to whistle like no other, if I let off the gas and idle it whistles... If I leave at idle for too long it whistles... If I coast at all it whistles. You get the point.
I've read it can be either a gasket of vacuum leak. I've checked the vac lines religiously and haven't found anything. I checked the torque on my exhaust manifold and it was perfect. I'm guessing it's likely a fried gasket, but does anyone have any experience with this noise.
Here is video of some dude's TJ that did the same thing.
<iframe width="560" height="315" src="//www.youtube.com/embed/VcxMbTQgbhs" frameborder="0" allowfullscreen></iframe>

definitely a vacuum leak, can be from any of several areas. Have you tried using carb cleaner sprayed around a little at a time when its whistling?

Unlit propane torch works too.

Also check the throttle body gasket on top of intake manifold too.

or a cracked manifold. A bit of time and a good light and some searching is in your future

I've heard of the manifold gaskets cracking, but not the manifold itself. It's been making the noise on a more scarce basis and when it does I don't have time to search it out. I'm really hoping it's just a vacuum leak and is easily fixed, otherwise it sounds like the most annoying supercharger known to man.

Bad intake-exhaust manifold gasket.

The manifold gasket is a thin, stamped metal backing, that is laminated with cardboard
fiber. In time, the cardboard degrades and gases enter via engine vacuum, and the thin
metal backing acts like a flute reed and generates a crazy whistle.

This is where having a stethoscope comes in handy to locate the whistle.

...or you can do this ...

On the next time when you hear that whistle, grab a spray bottle of water (set the nozzle
on "stream") - and squirt some water all along the joint where the intake manifold meets
the head. As soon as the whistle goes away, then you've located your leak.

Smearing on some RTV at that spot with a Q-tip will temporarily get rid of the whistle,
but you really need to change the gasket.

I would try to narrow down where the whistle is coming from. A mechanic's stethoscope can help out with that

TEST it with throttle cleaner or an unlit propane torch as suggested. All this jabbering is just speculation as to which of MANY things it COULD be.

3 minutes to diagnose. Max.