Rapid transaction log growth

I am trying to find the cause of rapid log growth on one database. Did not see anything unusual in Exmon or in the event logs on the DAG server. I ran through the steps in http://blogs.msdn.com/b/scottos/archive/2007/07/12/rough-and-tough-guide-to-identifying-patterns-in-ese-transaction-log-files.aspx and in about 130 log files found this line 723,058 times:

 0000000000 65535 f

I haven't found much searching for this. Does anyone know what it means?

Exchange 2010 build 14.3.123.4

Thanks!