Even if I don't do anything with the files in a .sparsebundle, just having a .sparsebundle open, it seems it is alive. Let me explain.
I regularly backup my main .sparsebundle (that sits on my Desktop) using rsync. I have an alias to do that, so every once in a while, I call that command to make sure everything is backed up properly to my external HDD. If I rsync multiple times in a row, at first, rsync updates many bands, then less, even less, and eventually it doesn't have anything to do anymore, all the bands are up-to-date. However, without using anything in the .sparsebundle on my Desktop, if I try to rsync again after e.g. 5 minutes, sometimes there are more bands to update! Why is that? Does the sparse bundle mechanism include, e.g. an OS background process that optimizes the bands silently?