Hi @Art
There’s not enough information to determine if it’s definitely caused by the mongod process, but off the top of my head, the mongod process does have a Full Time Diagnostic Data Capture process that records telemetry approximately every second. This data is typically used by MongoDB engineers to investigate issues with the server.
Another possibility that comes in mind is if the Database Profiler is active, it may record data periodically as well.
Also a replica set Primary would write a periodic noop into the oplog every ~10 seconds to refresh how up-to-date the Secondaries are for operational purposes.
Those are some processes that I can think of off the top of my head that does something with disk periodically. Having said that, it’s also possible that the activity was a combination of all the above plus some monitoring software external to mongod that you may have running. I guess as long as you don’t see any performance issues, it’s safe to ignore these events in the time being. Otherwise you may inadvertently turn off some process that’s important to the operation of the database 
Best regards
Kevin