After switching cables, re-installing drivers. I've got the clicking to stop. I unplugged the Avid 11 rack. Had it wired SPDIF out on 11 rack to SPDIF in on the 1800. The clue should have been the 11 Rack wasn't passing a signal to the 1800. Duh.....
And I'm definitely getting a new interface asap. I'd like to get the SSL Nucleus, but that's some serious coinage. So I'll probably end up with the Focusrite Clarette, or the PreSonus series 3 digital mixer.