Mitsubishi Repair: 94 Mitsubushi Galant ticking noise, mitsubishi galant, air circulation

Question
94 Mitsubishi Galant ES.  I get a very loud clicking noise whenever I press the button that controls the air circulation.   Switching from recirculate to fresh air flow thru causes the noise to occur.  Switching to recirculate stops the noise.  Is this a ECU/ECM issue (as discussed by Anthony) or something within the venting system catching on something else?  Thanks, jjj

Answer
John: You can have your car coded at any AutoZone for free and that would let you know if this from your computer or not. I would say it could be your fan causing the noise, so replacing the fan with a new one might stop the noise. Should get yourself a repair manual, can get one at any parts store around $20.00 and it will walk you through things. Hope this helps and good luck!