Nissan Repair: unit buzzing a 9, 1 over and over, chain idler, air doors

Question
93 Altima 2.4 DOHC A/T. Yesterday with the key on, motor running or not, a buzzing sound started. It buzzes 9 short times, pauses, then buzzes once, pauses and then repeats. It does this no matter what controls you flip,turn, or push. The car runs with no apparent problem. I've reset the ECM, no change. The buzzing, by feel, seems to be coming from the heater unit box above the ECM. A little pressure on the flapper control valve on the passenger side of the box seems to alter the sound a little. OBTW, the previous problem about not starting after replacing the head gasket is solved. The timing chain idler sprocket was 1/2 a link off for the upper chain. Resetting that raised our compression to about 120# dry and the car runs better than ever. Thanks for your help on that one.

Answer
Don,

My bet, without looking at it, would be that the heater box has a stepper motor going out on it.  I call it a stepper motor is what makes the air doors move.  Some cars use vacuum to move them and some use electric motors.  If the motor is failing is will buzz.  Now, it could be to do with the warning buzzer.  I did have one of those cause the problem you describe.  You will have to have someone work the key or controls and then crawl up under the dash and start looking.  A long screwdriver handel to your ear with the tip touching various parts until you isolate it will help too.