Help diagnosing clicking noise

[Scott Gilman]

Something new developed with my '91 200 TQ 20 valve and I'd appreciate  
any suggestions on what may be happening.  A clicking noise, which  
sounds just about like the clicking noise that the turn indicator  
makes is coming from behind the dash panel and one of the air vents,  
just to the left of the steering column.  The clicking sound is  
intermittent and only seems to start after the car has run for at  
least two hours.  Simultaneous with the clicking noise, the voltage  
gauge begins to fluctuate between 12 and 14 volts.  If the needle is  
not moving, there is no noise.  And the noise has nothing to do with  
moving the turn signal stalk.  The car starts okay and runs well in  
every other respect, just this latest phenomenon.  Anyone else come  
something similar?  TIA
Scott
NYC