This just started today, so it's not a cyclic thing that I know of....
yet.  Each day I set the timer and leave them open to air for 15-20 min. on the mid-day turning, usually, but sometimes I'll leave it open a little in the morning also while I'm brushing my teeth, etc. 
 
The felt didn't work, so I went ahead and turned it down to #1 on the controls and will monitor it there.  If they need tweaked down from there I'll try more insulation between the heat source and the eggs.  It's a warm day out and it's mildly warm in the room, but I have the window open to allow for air flow and the air itself is pretty cool.
 
I'll try to see if these spikes have a rhythm to them and report here on it.