write load while idle?

[Keith Freeman]

I have a 3-node cluster running 1.2.8, and with no clients connected 
(for about an hour) opscenter is showing a heartbeat-like pattern for 
total writes in the "Cluster Reads & Writes" panel on the dashboard 
ranging from about 10/sec to 26/sec.  Total reads on the other hand are 
showing a straight line hovering just barely above 0/sec.  There are no 
compactions, etc. (the logs are totally quiet).

Is this normal?  I'm new to cassandra so maybe this is normal but I 
couldn't find an explanation in the docs and it seems pretty high for an 
idle system.