More and more people are seeing this kind of problems. See http://forum.xda-developers.com/showthread.php?p=21840063#post21840063
It's a faulty USB connector on the phone, you should have it serviced, or change it yourself.
I bought this: http://www.ebay.com/itm/ws/eBayISAPI.dll?ViewItem&item=150713366355 and it fixed it.