The mx518 mouse I got from newegg (http://www.newegg.com/Product/Product.aspx?Item=N82E16826104178&Tpk=mx518) made a high-pitched humming sound, though I had it for too long and they refused to return it. So I got ahold of logitech and had them send me a new one, and it made the same high-pitched hum, though it's not quite as loud, it's still very annoying. Is the model itself dysfunctional, is the problem being caused by something other than just the mouse, or am I just unlucky?