Yeah, there's no wires going to them. They're ear protection.

Edit: Nor antenna. Probably not wireless headphones.

Ear protection is the obvious answer, and I included it in the options. The other option is the one you might want to believe (free choice of music). The last one is suggested as a what-if alternative. Partly because it's an interesting story (at least the first part about the Mana system is), and partly because if anywhere is going to implement a Mana-like system, Google has the drive to do new weird controlling things, the technical expertise to have a massive central task and employee management system, and a their simplified yet very large server room setup sounds like a good place for that kind of thing to be useful to cut down on skilled worker requirements.

Saying "probably ear protection" is rather missing the point of my post, and getting three upvotes for it suggests that I wasn't at all clear enough.

Point being: imagine the kerfuffle if it turned out he was being guided by an automaton task master using wireless headphones and systemic feedback from many smart sensors in the style of the coming Google power grid monitoring system - picking up a server from repair bay D2 detected, entering the server room detected, sliding a server detected and the server's details taken by RFID'd and putting a new one in, details from RFID, booted and configured and brought online automatically, old server returned and asset tracked.

Google already design their own servers and server rooms, they track power usage and memory errors and disk failures and have kernel modifications to track resource usage by program. It's not that far out, and is the sort of major thing they might do quietly which might only leak out initially by a slightly odd picture or a disgruntled insider comment.