I have that clicking noise too whenever I turn off the aquarium lights...I'm guessing it is caused by small pistol shrimps/snapping shrimps that comes with the live rock.
My niger does the same think, usually after feeding time when he swims up to the top of the tank and making the clicking noise with his mouth. Its pretty cool and it has gone on for a while so I wouldn't get worried.
very common for the trigger to make noises they i belive i read it was a form of comunication so it is more than likely that it is basically just giving u notice it is still there
I dont have exp. w/ triggers so I cant comment on that, but I was wondering if you have a flame scallop that is it ..if not do you have any hermits,their shells also do this as they hit the glass..just another thought