I just got a 2004 Mustang with a 3.9 V6 and 5 speed and several times now I've heard a "chirping" sound when I get over 45 mph. It sounds like it's under the dash some where but can't tell for sure. A mechanic said it's probably the idle air control valve, he's had to replace several that did this. I heard the exact same noise while test driving another 04 Mustang too. It's still under warranty but they won't replace any parts till they hear it and of coarse it was fine when I took it in. Anyone know what is making that noise? I want to get this fixed before the warranty is up plus it's annoying, sounds like a bird in the car (lol)