'08 pt cruiser rear power windows went down by themselves?

my aunt was driving yesterday and she said she heard a weird noise(from what i can remember her explaining me the noise it was a low pitch sound versus a high pitch sound, at least that's the best i can explain it as far as typing a sound) anyway she hears the sound and all of the sudden both her rear driver and passenger side windows both go down simultaneously by themselves and now they wont go back up --- any suggestions as to the problem? [bad regulator maybe] by the way the front two windows power down and up fine. any opinions surely appreciated!!!! thanks guys!