Strange resource Content Download pattern

[vmichnowicz]

I have been noticing a strange Content Download time across all of the resources on my site. This pattern affects all resources on my server (JavaScript, images, pages etc...), however, it does not affect resources on other servers (Google Analytics JavaScript). To help visualize, here is the Content Download time of a fairly static HTML page on our site:

   

As you can see the Content Download time displays a very distinct pattern over time. I am wondering what the cause for this pattern could be. We have not been toggling anything on our server on and off, and this pattern is visible across all static and dynamic assets so this is not something database or back-end code related.

Is there anything WPT-related that could explain this pattern?