Check and see if the backup options got checked at some point to include imported items. My files were growing about 40 MB/D when I was including imports, and I was not scanning in old charts.
There are several threads here about backup plans, and they are well worth reading. It will take several cuts at the apple to digest all the things discussed, but it will be well worth it. A good backup plan is crucial, and the AC backup utility is only one small part.
