SSR - Why are OS drive incremental backups so big? Windows SBS

Hello,

I work with a number of servers that use BESR/SSR.  I have noticed that some have daily incrementals that are 2GB, while others are 11GB.  SBS servers seem to be the big culprit in this, however they don't all do it.  I don't think it is a heavily used share as all our user shares are on the data volume.  I'm trying to isolate what it could be by disabling different DB's/services, but not getting anywhere fast.  

Any Ideas?

Thanks!