[Zope] data file keeps growing

I have the /Members folder of a CMF site mounted in its own separate ZODB called MemberData.fs. The file keeps growing at an alarming rate of about 400MB a day until it eventually reaches the 2GB limit them i get loads of MemberData.fs.trxxxx files There's no extra data explicitly being put into the member homes, if i go to pack database it reduces back to about 50MB Does anyone have the slightest clue what could be going on?!?!?!?!?