This is a long shot, but I had exact same symptoms last week and clicking was coming from fuse box under pass. dash.
More specifically it was coming from a relay, I removed the relay and clicking stopped, so I tested the relay and it tested good!
Anyway, turned out to be the interior light vertical slider switch on my dash. (When it is slid all the way up it clicks relay and turns on interior lighting)
The slider was on the event horizon of interior lights on/off and was clicking the relay repeatedly.)
This also killed my battery too by way of flickin on my interiors while I was away from my rig.
Hope it's something this simple for you, worth a look anyway