Chevrolet Repair: 94 Suburban clapping noise, vacuum leak, noise question

Question
QUESTION: when turning car on or off, the heater box inside under the glove box makes a clapping noise for 30 seconds, then stops.

ANSWER: This is a common problem from about 1991 to 1996 in most 1500 and 2500 models. The problem is the recirculate air from cabin flapper inside the duct work. I haven't fixed the problem myself but I would suggest to take it to the professionals on this one if your not clear with the cooling and heating components.

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QUESTION: Can you please tell me what the problem is exactly.  Is it a vacuum leak, a bad relay, a component that needs to be replaced, or what?

Thanks.

Answer
I'm sorry. Usually, the problem has to do with a plastic gear drive system. What happens is the gears get wore out and the flapper will catch on something, this is what causes the clicking noise. Usually they get in there and replace some of the moving components. Like I said, I haven't had the joy of working on this problem myself so I can't tell you exactly what to do or how to fix it.