C: drive slowly running out of space on Exchange 2013 CU2

Here is my Setup

Exchange 2013 CU2 running CAS/MB/UM roles.

The page file, and databases are running on a separate drive/LUN. No mailbox databases are on the C: drive.

The only thing on the C: drive is the OS, Exchange, and Transport logs. The transport log/queue folder is not growing.

I am losing about 1GB of free space on the C: drive every few days. What on the Exchange server cause it to keep losing space so quickly?

http://jaworskiblog.com