My nexus S has a problem. After the phone has been sitting and I unlock the screen the volume up and down bar appears and the ringer volume goes up and down and to vibrate without me touching any buttons. It's like it is possessed. When I try to turn the volume up it turns it down and starts vibrating. After pushing the home button it will stop and may not do it again for a few hours. This has happened over five times now. I've turned the phone off and on and it still does it, but not with reptition like and app is doing it, it happens so random. Any ideas??