[aceyx]

Try shutting down the engine while rolling; it should help you narrow down where the noise is coming from (at the wheels or directly underneath). I hope I don't have to tell you that this will make braking and turning much more difficult, and to only turn the key back one click or the wheel will lock.

I would also try spinning the rear wheels. Based on the second description of the sound, it could be a stuck parking brake. It could make sense that if your parking brake is too tight, the rotors would shrink around the shoes to create constant contact.