If you have rear drum brakes, you may be hearing the shoes sliding on the backing plates. Each shoe rides on three "lands" or raised spots. Pull each shoe away just enough to brush in a light coating of high-temperature brake grease. I've also used "Spray White Lube" from the Chrysler dealer which is a lithium-based grease. That's not what it's meant for and it won't last as long, but it's quick.

There is a tool you might be able to borrow or rent from an auto parts store that borrows them called the "Chassis Ear". It is a set of six microphones, a switch box, and headphones. You clip the microphones to suspect points, then drive around while listening with the headphones. You can move the microphones around to zero in on the source of the noise. Be aware that many mechanics have never seen or even heard of this tool. Suspension and alignment mechanics use it to find rattles, squeaks, and other noises.