SQL Server tuning: Disk queue to OS drive: How to optimize?

I expect to see the disk queue move on the data, tempdb, log and backup volumes.

I do not expect to see the OS drive (C:) which has zero SQL files present, show disk queue impact.

Assume it is to the OS paging file, or ?

Suggestions on how to chase?

This is SQL 2014 on Win2012-R2/