mms sound playing after phonecalls

a lady at my office has had this twice with her 8520 curve. we dont know how to fix it and now i have it. i received an mms which i forwarded. shortly thereafter i received a call and once i put the call down the mms sound plays. this happens basically after every time my phone rings. if i miss the call the mms tone plays once my phone is done ringing. otherwise once i put the call down. how do i stop it and how do i prevent this from happening again? help please its awful :eek: