I've seen this on our lab machine last December and again in March and April. It happens about every 55 minutes. I can see no reason why it starts or stops. Just for grins, would one of you try /etc/init.d/postgresql92 rebuild (you must do it on both devices if you're in HA)? CAUTION - this re-initializes all of the PostgreSQL databases, so you lose all reporting data and (maybe) graphs. Logs are not affected.
Cheers - Bob