There's been a lot of talk of the volume bug on the Samsung Galaxy Nexus ever since it surfaced over at XDA several days ago where some users reported that the phone would automatically change the volume and mute. The problem was documented when the Galaxy Nexus is placed close to another phone that's making a call on the 900MHz GSM band. Initially they thought that the Galaxy Nexus had inadequate shielding, and the interference was causing the handset to rapidly trigger the volume down button...
After gaining much attention on Google's Bug Tracker Site, Android Police reached out to Android PR and got the following response:
Well there you have it folks, looks like the volume bug on the Samsung Galaxy Nexus is a software issue and not hardware related afterall. No word yet on when the patch will be available but it's good to know that Google is already working on a fix.
Source: Galaxy Nexus Forum via Android Police