When I turn on the ignition and also shut it off, there is a loud ticking noise behind the glove box area. I think it maybe a servo on the vent door, it lasts about 10 seconds and then stops. Can this be unplugged without effecting the heat and a/c? By the way heat and a/c works fine now.

I am having the same problem with my truck,IT DRIVES ME CRAZY!!!I tracked it down to the heater box behind the blower motor,I can push up on the fins and make the noise stop when it is tapping.If you find out what it is please let me know.

Anyone out there who knows the problem please let us know.Thanks Rick.

same problem . no known sollution . i thought that was only in my truck.
I hope somebody finds a sollution.

Hello again,I did some research online and i found someone that had this problem fixed,The problem is a plastic heater control gear behind the blower motor that gets stripped out with age,This gear opens and closes the vend door in the heater box.This is a $50.00 part from the dealer and it takes about two hours to change according to the chilton manual (the dash has to be pelled back to get the blower motor out and the gear is behind that).I am going to tackle the job soon and i will post more detailed instructions when i am done.Hope this helps Rick.

sounds like your on the right track. please let me know how it goes. this is driving me nuts.

NO MORE TICKING NOISE!!!

Ok guys if you do not want to spend 2-6 hours tearing out the heater box to peplace this $50.00 part i have a cheap fix (now don't laugh).If you lay on your back on the passengers side floor and feel behind the blower motor you will find spring loaded plastic vent doors,I found that when i apply slight pressure to the bottom of these doors when the ticking thing is going on i can make the noise stop!!!you will have to experiment to see which door makes the noise stop i believe there are four different ones under there.Ok now find a wooden clothes pin and pull it apart,Use one of the wooden halves and have someone turn the key on and off so you can hear the ticking and slide the clothes pin in the crack where the plastic door opens until the ticking stops (the only thing this may cause is a little extra floor heat when blower is on) .Hey it works NO MORE TICKING NOISE and you cannot see it when installed.My heat works fine in all positions on the heater control and i figure i saved myself $200.00.I figure this is not how your friendly GM dealer would want you to fix it but i figured it sure is a easier and les expensive way out.My truck is a 1993 K2500 5.7 W/AC but i think this will work on all GM/CHEVY models with this noisy problem.

I tried it and it worked!!! This was a 5 minute fix. Thanks alot!!

Way to go guys. Do what you have to do and keep your truck out of the STEALERSHIP!!! I have a 91 GMC and I'll keep this in mind if it happens to me. Thanks. Good work!!
Kevin

I have this same problem. I put small peice of wood in the vent door and it stops it just fine. Only one problem being on cold days (under 40) the clicking comes back. If I could just unplug or disable this dreaded door I would be much happier.
Anyone tried this approach. It just doesn't seem worth taking all apart and putting a 50$ part in since the rest of the system is fine.

Hey good info guys! But a suggestion about the "quick fix". I just bought a 93 GMC half ton truck. It had two noises, one was the clicking noise that has been described here and the other was a horrible fan noise. The horrible fan noise went on until it spit out a small wooden block.

The lesson here: you may want to find a way to fasten that wooden clothes pin in place so it doesn't fall into a place where it shouldn't be.

There is a wiring connector on the left side of heater box where the blower motor is mounted. The noise will stop when this is disconnected. When disconnected the outside air duct will stay closed all the time, but no noise.