well lately when i drive with my radio off and windows down i can hear this like grinding noise from i believe the rear of my car..like maybe something was rubbing or rusted..i'm not sure..anyone have any ideas..i don't believe it's my brakes because i just got them changed and it doesnt make noise when i step on the breaks.only when i'm moving slowly..when i drive fast i dnt think i can hear it or it isn't making noise...thanks