[patrickt]

First, put her up on a lift and do a thorough inspection underneath for anything rubbing somehow. Assuming you don't find anything out of line, then...

Second, take her for a drive until the squeak is nice and obvious, then pull her in to your garage and put her up in the air, with the trans in neutral, and spin all four wheels by hand. Listen and feel for a squeak. If the squeak is periodic, in time with a wheel rotation, then it almost has to be a part that is rotating as well, like a bearing, a u-joint, hubs, rotors, or that is stationary and that has a part rotating around it. But if it comes, and then goes, presumably because of thermal expansion, then it's something that is just barely touching something else -- like a cotter pin that is just barely nicking a rotating part and creating a "squeak" when it does. Situations like that almost always leave witness marks that jump right out at you when you finally stumble across them.