Thats weird if its not the coins changing. What could be the problem? When it happens, its for 5-10 seconds each time.
I am using MultiMiner to monitor my rigs which are in another network and although I have a back up pool, it doesnt report as the eu pool being down. So it does not change pool.
I think you have a power issue, the GPU load is unaffected by coin switching. Do you have a kill-a-watt? I would check exactly how much power you are pulling from each of your PSUs, you might be overloading them. Also what is the max AMP of your circuit you are running, 5 rigs on? (you said 5 right?) I had a 50amp circuit wired just for my rigs that run around 2000 watts.
All three of my rigs are doing this now as well. Different locations, different setups, all <6 months old. Probably started doing this maybe with in the last week.