When I'm looking at my container engine logs, I see a lot of warnings. After digging a bit further, I realized those errors are actually just logs from heapster.
I believe this is due to the log starting by I0730
My kubernetes cluster is using version: 1.3.2
That's because Heapster is logging to stderr rather than stdout. Starting in Kubernetes 1.3, logs written to stdout got tagged with the INFO severity and logs written to stderr got tagged with the ERROR severity.
That clearly isn't working well for Heapster since it's sending all of its logs to stderr. I've opened up https://github.com/kubernetes/kubernetes/issues/29862 to track improving this.