so regular as probably to be caused by someone calling System.gc() on a timer thread. Does that pattern hold for the rest of the log? It could be RMI, but that's not the default interval. (Use -Dsun.rmi.dgc.client.gcInterval= and -Dsun.rmi.dgc.server.gcInterval= to change the intervals.) You could try running with -XX:+DisableExplicitGC to see if that turns those full collections off, but then you'll really want to chase down why someone thought they were necessary.
$ dc 10k 761.201 693.301 - p 67.900 693.301 625.461 - p 67.840