We see more and more customers enabling Windows deduplication within a VM to save space on the file servers. Even more with Windows 2016 this will become more and more the standard.

With deduplication enabled you will see a ~20x higher change rate every 28 days at the block level backups (e.g. Veeam). The root cause is the garbage collection run of the Windows deduplication engine.

You can find more informations here:
http://social.technet.microsoft.com/wiki/contents/articles/31178.deduplication-garbage-collection-overview.aspx

…and can discuss the solutions here:
https://forums.veeam.com/post193743.html#p193743