Our initial impression of cavity power fluctuations was that temperature fluctuations in the EAOMs were the cause.  To check this, I made some REFL DC monitors yesterday.
Plotted is one hour of data from today.  Some notes:
1) TRANS DC and REFL DC for both cavites are breathing together every fifteen minutes, and are anticorrelated (one goes up, the other goes down). 
2) The temperature monitors are not fluctuating with the same regularity as the power monitors.
3) The REFL DC for the north PMC is fluctuating with temperature

This leads me to believe our power fluctuations are caused by changes of alignment into the cavities from the air springs holding up our vacuum can. 
Right now, the air springs are hooked up to the wall.  There is probably some pressure regulator which switches on and off every fifteen minutes.  To fix this, I'm going to switch the vacuum air springs over to our nitrogen cylinder we have in the lab and see if the fluctuations go away.