sudden drop in comp factor

I've been writing Oracle backups via RMAN and Networker to Data Domain for several years. The total comp factor normally hovers around 8x. About a week ago, it dropped to around 3x.

An oddity I see looking at the DD "Daily Written" 60-day chart: my pre-comp written is nearly a flat line. Up until a week ago, my post-comp written would vary a bit, and thus my comp factor would vary between about 6x and 12x. For the past week, my pre-comp is the same as ever, but my post-comp is nearly a flat line, and at a much higher level. So my comp factor is now also nearly a flat line, at a much lower level than before.

I know of no changes to the database server, to Networker, or to Data Domain. At the current rate, my DD will be full in a matter of days. Any ideas on how to troubleshoot?