I can't speak so much on what may have caused this. There might be a SQL job that is failing to truncate the logs. There is a way to fix these and shrink them manually. Should you need this, do the following in a command window.
How to shrink UnityDB/ReportDb if it grows too large:
1. Bring up command prompt
2. osql -E
3. use unitydb
4. go
5. backup log unitydb with no_log
6. go
7. dbcc shrinkdatabase(unitydb)
8. go
9. exit
To shrink the ReportDB, just do the same above commands and substitute ReportDB for UnityDb on all lines.
Tray