When looking at the optical lever diodes recently I noticed that the ITMX diode sum seemed to be dropping and rising very regularly, with a period of approximately 6 seconds.  The attached image shows two minutes of data for the four indivual ITMX diode segments along with their sum.  It was not obvious to my eyes that the four segments would add up to equal the sum (it seemed unlikely) but Keita added the four signals together and it did in fact result in the sum as we see it on the plots.  So the sum channel is being added properly, however we still do not know why it is rising and dropping as it is.  I looked at old data to try and see when this behavior started it and it looks like this has been happening for a long time.  This pattern was visible in the data for all of 2015.  It can be clearly seen in data back from January of this year.  I did not see this behavior in the other optical lever diode channels.