Strange White Marking

[downhillskier]

Hello, I wanted to know if anyone else has this issue. On the back of the Sansa Fuze, where the product key is, I found some kind weird white stuff on it (granted I’ve had the Fuze for 2 years), but I didn’t notice this until now. So I took my finger and tried to rub it off because I thought maybe it was a sticker. Instead of coming off the white mark became bigger and bigger until it almost totally took up the product key box. Does anybody know what this is? It’s very strange…