Problem(s) Encountered:

Templeton's performance is degrading, in the form of pickup-like pattern noise with amplitude of several ADU, which is quite a few electrons.  This stamps itself on faint spectra and makes it very hard to work on fainter objects -- you never know if that 20-min exposure is going to be any good.  It's as bad as Echelle was getting, and appears to be a very similar issue.  I doubt if much can be done about it, and I may be able to filter some of it out with enough effort, but I'd appreciate it if it's possible to have a look at it to see if anything obvious is wrong.  I  will try to remember to turn the controller off a the end of the night to see if resting it might help.  

Solution:

Power line filter was swapped out for a new unit. Per observer: "The pattern noise is much improved, often absent and when present much less intrusive."