I havn't use my ipod maybe twice, tonight I picked it up and I felt it cave in a small spot. Right behind the screen, so it has a small dent. . The screen is ok their no marks or srapes.. . Its perfect, how did this happen all I did was grab it from the back to take it out of case and its has a small caved in looks like it dent. What should i do and what kind of material is this the back made of