Vaxee E1 rattling noise

hello, I just got a vaxee e1, and whenever I lift and put the mouse back down or tap the front edge on the pad, I hear a kind of rattling noise that I don't know where it's coming from. there's no rattling noise if I shake the mouse and it's not there if I tap the back edge of the mouse, only the front edge. Is this normal? Or is there something wrong? Thanks.