What's process "find" owned by "nobody" that's hogging my CPU periodically?

Is Spotlight indexing your disk at the time?

There are a number of scripts that the system runs at periodic intervals (daily, weekly or monthly) for various forms of housekeeping. One of these tasks is updating and maintaining the "locate" database, which is referenced by the command line tool ' locate', which allows the location of items to be returned almost immediately based on a match of a search term to a full or partial path. The process of updating the database includes using ' find' to scan the hard drive to see what is there, and I suspect that is what you are seeing.

The ' locate' command and database is available to everyone on the computer, but unlike eg. "Spotlight", there is no mechanism to restrict what search results are returned to whom on the basis of whether or not they have the privileges to that item. For this reason, the ' find' is run as the unprivileged user "nobody" so that eg. the private contents of users' "home" folders aren't indexed.