Mine just fell off! Don't know where or when as it was nowheres to be found, two kids at my daughter's school have had the same thing happen. I always thought the volume slider was a bit on the dodgy side, very loose and wobbly. In fact that was the only fault I could find with it, once I figured out how to put music on it in the first place. Sony have said they will only repair it under guarantee if it was a fault with the product and not 'accidental damage'. I don't know how they plan on ascertaining this as I have no clue what dislodged the damn thing myself.
