After the hints executor finishes sending hints, another hints file is created for the same host, which is then processed on the next go around. This continues indefinitely. The new hint files are empty, so there shouldn't be any network traffic. However, there's still unnecessary hint activity, and the hint crc file isn't deleted in the 3.0 branch after hints are dispatched (but is in trunk), so any hint activity will trigger ~8640 files being created per day until the node is restarted. Restarting the node fixes the problem, after the existing hint files are processed.
This can be duplicated on cassandra-3.0 to trunk with this script: https://gist.github.com/bdeggleston/13fbb9e70c0c0bd277c7