Pat, I saw the two bias images with cooling off/on yesterday and I am not sure what to make out of it
The cooling stays on or off during the duration of the whole frame reading, it does not get switched. From that point of view there should be no noise.
Can you try using a different power supply? Perhaps when it is loaded (cooling on) it puts out more noise? Or can you ask someone else with a working cooling to do the same test and report.
Also there seems to be a pattern in the right image, which, again, I cannot explain
The frames are read line by line but the pattern seems to follow in rows as well. This would indicate that the sensor itself was affected by whatever the source of "noise" is.
Interesting...