Hi,
I have the same issue (but with queues RRD) on my 2.1.5-RELEASE (amd64) built on Mon Aug 25 07:44:45 EDT 2014
The wan connexion is 100Mbps symetric, and there were no clients at all in the lan network (both are different vlans on same interface), since the pikes on the graphs seems synchronized, something is going on somehere .. just can't figure what it is. Strangely, no spikes at all on the trafic graphs.
I know I'm in the wrong category, but it's the only topic I found about this. Note that I saw those kind of artifact as long as I used pfsense (from version 1.8 or 1.9 I think)
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