I get clicking sound from our electric water heater as well. it lasts for a while, then stops...then starts again, etc. we recently had technician out who said it needed to be cut back on the setting for temperature, it was set at about 132 degress...he turned it back, I believe to 120 degrees. We bought it in 1996. Only name I see is on the control box, amf paragon? says 50 gal capacity. Is the clicking sound something normal for the process of keeping water supply heated up as it cools down or something? Or could this be a problem due to age. I saw in one reply to someone else that sediment could be built up and needs flushing? I am afraid to mess with it, so wonder how critical something like this is?
For starters, I'd suggest you shut down the heater, drain it completely, and replace both electrodes.
The danger with a water heater this old is that in draining it and dislodging sediment within you could expose small leaks.
At 16 years old, I hate to say it, but you'll probably find it more efficient just to replace it.