I ordered an MX518 a couple weeks ago and it's been working great so far, apart from the fact that it's letting out a very high pitch whine, which is very quiet but very noticable when you have no music playing etc. It's quiet enough to be able to ignore it although you're occasionally reminded of it. At first I thought it was simply my ears ringing for days, and kept checking my speakers/monitor/pc etc. too to see if it was those, (aswell as various clocks nearby) but couldnt find the whining, but have now found it coming from the mouse. Why would it be doing this?