What is time machine backing up? Is there a way to find out what time machine is backing up?

My time machine has been running fine, but it suddenly started to back-up 20GB a few days ago when I have not changed that much since last back-up.

This morning it started to back-up 14Mb, but I have not used it since it's last back up at 00.01 am.

Thanks,

Linda
There are two tools I know of that do this: (1) BackupLoupe (which is a GUI application) and (2) timedog (command-line Perl script).