If it's just a slight squealing I wouldn't worry about it. Lots of things can cause that...dirt, brake dust, brake glaze, temperature, etc. You could try doing a few hard stops from 30 MPH or so. SOmetimes that will remove the glaze if that's what's causing the noise. usually glazing is caused by riding the brakes though or braking too lightly all the time. You aren't doing that are you?