chirping noise under Hood?

When I put my brakes on I get a chirping noise from under the hood, I don't think it's the wear thingies on the disc brake pads. It kinda sounds like a idler pully squeak. I suspect that brake assist thing next to the power brake booster? Anybody had this little birdie chirping?
Can't find it? :banghead:

Thanks
Tim
2003 YUKON SLT 42K miles White w/Tan DVD

we have a denali 04
whenever my mom is at a very low speed and braking and is turning she hears a high-piched noise
coming from what my dad things are the brakes. We can't see what it is. is this the same squeak that your hearing?

Nope it's not the wear sensors, looked at pads this weekend plently of pad left. It may be the metalic pads may have to go for the ceramic pads
Tim

I have a chirping sound from my 1999 Yukon, but it occurs when running over small bumps. It is in the right light assembly. If yours is the same, just pound your fist around your light assembly a few times, and you'll hear it. Just a nuisance.

This might sound weird, but I had the same problem in my 2003 Yukon. I would notice a chirping noise when braking ... the key was it would happen when I let off the gas. As it turned out, it was the PCV valve. The stock PCV has too small a hole in it and that's where the chirping was coming from.

A quick trip to Autozone for a couple dollar PCV valve fixed the problem.

Hope this helps.