Relay? I used to work on telephone, fire, and security systems...
many, many years ago, before integrated circuits... thousands of
relays... when one starts to go bad, before it completely dies, it'll
usually "chatter"... sometimes for a bit, and then stop, and so on.....
what side of the dash board is the "clicking noise" coming from.....
there are also solenoids for your HVAC system and a control
module for that as well..... but..... the real culprit might be your
"chime module"..... it does a lot more than just "chime"..... you can
disconnect it and clean the contacts on it..... they often get
corroded.... mine is on the passenger side under the dash..... let us
know what you find out..... i believe mystery noisy things under the
dash, are just as or even more so, annoying as things chattering
under the hood..... ~ john b. ~ "Even if you are on the right track,
you'll get run over if you just sit there" ~ Will Rogers.