In a replicaset of 3 idle nodes, when one node is unavailable, the remaining two nodes' processes spike to about 60%-80% CPU usage. The spikes seem to occur in an alternating fashion once a second.

Bringing the missing node back online results in all nodes' processes returning to a consistent <1% cpu usage.

The attached graph shows the processes spiking on CPU #2 (right most graph) and then returning to normal at the end when the 3rd node is brought back online.