I suppose you could run your car without the accessory belt...if it's already cold you won't need your water pump and since you won't be moving you won't need P/S. Just sounds like a funny test to me.
That does sound like the tensioner is not working, though...or one of the other pullies is dying.

 

So, I replaced the belt. It's better, but still definitely squeaky, coming from the bottom-ish end of the passenger side engine.

The tensioner seemed OK, seemed appropriately difficult to move it. The auto part store tried to give me a belt (Autozone Part Number: 6PK2100, effective length of 82.75") that was shorter than what was originally on the car (OEM: 6PK2120, effective length of 83.5").

I went ahead and tried to put on the short belt but gave up on it. The OEM sized belt went on very easily (had to wiggly it onto the crank pulley with the tensioner all the way back, but it only took about 90 seconds to get the thing on).

So, am I just a sissy who needs to go back out there and put on the shorter belt?

 

Ugh. Found the problem. Belt? Nope. Tensioner? Nope. Idler? Nope. AC Compressor? Nope.

A bolt at the back of the cat's upper heat shield pulled through the shield, leaving the back of the shield to freely vibrate. Would have thought that metal vibration would be more of a "rattle" than a banshee squeal, but at least now I can make it go away.

 

Oh wow ok. Yeah, it's difficult for people online to diagnose things when we can't hear/see. The way you described it definitely sounded like a belt. At least you solved it and a serpentine belt isn't expensive anyways.

 

The sad thing is that I originally thought it was the cat bracket based on on-line descriptions of the problem, but neither piece was broken. Plus, it just sounded like a belt problem to me, so I wasted three days trouble shooting a problem with the belt and pulley system when I just need a washer for a heat shield. I feel ridiculous, but at least the gremlin's been flushed out into the open.

 

Depending on the frequency of the vibration (how fast) it can sound like a squeal instead of a tapping, or rattling. Thats something learned over time, and not very easy to pick up on.

 

Ah thank you I have the same problem squeal on start up and my tensioner seem fine. Im going to check this to see if maybe this is it. I also changed out the belt and that didnt fix it.

 

Warning on those tensioners:

I had the squeal for 30k miles, thought it was a noisy belt. Finally the belt melted and wrapped its cords INTO my A/C clutch. Took me 3 hours under the car with dental picks to get it all out. Liquid rubber filled every groove of every serp pulley.

Change the tensioner!