2006 Xb.
Last week I started having a slipping belt noise start. It only happens when the engine is idling at a light, then gets worse just as I take off but then stops and runs fine till I put it in neutral and pull up to a light or a stop sign. I replaced both belts today and it still does the same thing. I popped the hood and every pulley is moving fine, as are both belts, but the noise is awful. There are no other issues, or fluids leaking, or any lights going off. When the belts were off, all the pulleys seemed to spin just fine. It sounded more like it was coming from the power steering pump area. I turned the wheel both ways and it seemed slightly louder with the added load.
I am thinking it may be the pump, but never heard a power steering pump sound like a squealing belt.

 

This post looks familiar

<3 a Skyon

 

I had the same problem and tried tightening it a couple times before I replaced the serpentine belt with a Dayco belt. It's supposed to be a special design to prevent it from slipping. I did have to tighten it again about a month later, but it's been 5 months since then, and I haven't heard it squeal.

Here's the link to the belt. You might find it a bit cheaper somewhere else, but there's a video there that explains how it works.

http://www.autozone.com/autozone/par...50124_0_15795_

 

Reduce your electrical load when at idle, no heater, no brake, lights off and then rev the engine a little and then let it idle and see if the squeal goes away. Alternator load is usually the problem and you probably polished the pulley so much that even with a new belt it slips.

 

Has anyone tried using some low grit sandpaper to scuff the pully that is slipping to give the belt some traction? I have a 2005 Scion xA that is having the same issues, new belts that are nice and tight but it still squeals like a pig and I think I know which pully is giving me issues and was contemplating doing this.