I have noticed the clicking sound too on/in my '98 70.
Is the clicking sound is originating from the inside of the vehicle, or outside (like under the hood) ?
Mine seems to be coming from underneath the dash (driver's side, under the dash directly beneath the windshield). It's a very sharp click -- actually, a series of sharp clicks, 2-3 seconds apart, 6 or 7 clicks in duration.

For some reason I think of it as coming from the climate control system because it only happens when I'm heating or cooling. I imagine it to be an air or temperature sensor, but who knows. I've heard it for years and have never tried to get it diagnosed. Has presented no problems. I think of it as one of the cars little daemons.