I have recently upgraded our web gateway software from 7.2.x to 126.96.36.199.0 and until now I have never received this warning and since the upgrade I am seeing it randomly. The upgrade to 7.3 was done last Friday morning (in time for the Canada vs. U.S. hockey game) and I did see it happen a couple of times during the game which I would expect as our internet line was maxed out. I didn't think too much about it but this morning I came in and looked at log and I see that this morning at 4:39am the warning popped up again (3.27/3.00) 2 times in 91 seconds.
I looked at the graphs and there is no spikes and nothing that I can see. Looking at the system utilization graph it shows that CPU was only 1% used.
I had been running 7.2 for over a year with no issues and no warnings such as this.