Name that noise!

So my TJ started making this dying yak sound the other day. It usually only happens when it's frikkin' cold out. It's a high pitch moan coming from the passenger side of the engine compartment, and gets louder as the RPM's increase. It's really pretty embarrassing.

Does it happen as long as the Jeep is on, or does it go away when it gets warmer?

It goes away once it warms up to temp.

I think it may be the alternator. Best thing to do would be to start it, pop the hood, and then see if you can trace the sound while it's running.

Also check the idler tensioner pulley. $20 at AutoZone. Loosen up the belt and swap a new one in.

Did mine last February.

There is a good chance that you have a tensioner or idler pulley bearing that is in need of replacement but it does not hurt to check fan clutch while you are there.
Check the fan clutch while you are there (with engine off) grasp a fan blade at 3 oclock and 9 oclock position and wiggle to see if there is play in it.
Also spin it (with belt still on and tight) and listen for bearing noise after engine gets up to operating temp.

Spin alternator with belt off and listen for bearing noise, I have gone through three of them.
If you have ac spin clutch bearing also.
And if you do have ac, does noise go away when you put heater on defrost while running and engine cold?
Anyways, spin everything there and give a good listen to it.

Jarret, did you find out what was making that noise?

Nope, it stopped all by itself once the temps stopped dipping so low. It hasn't happened since I posted the thread.

When it did happen though, Mark, turning the heater on and off was the first thing I tried, but it didn't affect anything.

Jarret,
Just remove the belt and spin everything and go from there.
Maybe do that while it is kinda mild out even if it is not doing it right now.
If you do find something wrong you could take care of it now.
It could save you from having to do it in the freezing cold.