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Discussion Starter #1
No luck searching this, but I expect it's been discussed before. When the engine is off, even for weeks, there is this occasional brief noise under the dash. It sounds like a servo-motor whine and lasts about two seconds. I'm guessing it's an HVAC door, but why?
 

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Yes, I have another Dodge product, Caravan minivan, and it does the same thing. But only once every time the ignition is turned off. Disconcerting because it happens a little while after the ignition is off.

It does sound like a servo motor. And then there's a related noise, like that of a flap opening or closing.

BUT I don't think it repeats without the ignition being turned on again. Or maybe I haven't noticed it. I've slept plenty in the minivan and notice it happening only once per ignition off. I would be even more worrisome if it happens again and again without me knowing or being involved.
 
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Discussion Starter #4 (Edited)
It definitely happens more than once after the engine is turn off. The van hasn't run in several weeks now, but I hear it just about every day since I'm working in the van a lot. Maybe 2-3 times a day max, depending on how much time I spend in the van. It isn't loud, so it would be easy to miss in a city noise environment. But we live out in the woods where it's dead quiet much of the time (that or chain saws). I'm more curious than worried.

EDIT: OK, I just did some more googling, outside the forum and PMs this time. Similar under-dash noises are common in Dodge Ram trucks. The consensus is that most are normal. The HVAC blend door seems to be the primary culprit. But I still couldn't find a reason for it's continued/repeated operation even when the engine is off.

I even found
, but not mine. The videos sound more like hammering or gears stripping. Mine is a continuous servo whine that changes pitch at the end as it meets resistance. Maybe the blend doors in the videos are jammed. Something to look forward to, eh?
 

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Perhaps there is a setting for the blend and or routing doors that makes it more prone to cycle when off. I have heard it a couple of times.
 

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Here's a link to a post of a guy who observed this in another Dodge product (a Jeep).

http://www.wranglerforum.com/f274/2012-jku-noise-of-something-moving-after-car-shutoff-126077.html#post28081017

He's thinking it is linked to the opening and closing of one of the doors and not the ignition. Perhaps this might explain how the OP has noticed that the noise happens even though the car hasn't been started in weeks. i.e. the OP opened at least one of the doors to work on the van, but never needed to start it, and then the mysterious noise happens.
 
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Discussion Starter #7 (Edited)
Ahhh! Now we're getting somewhere. Yes, I do open and close the back doors a lot, especially this winter with a space heater going. I'll start paying attention to see if it only happens once between door openings.

I'd still like to know what purpose it serves. The Wrangler Forum poster said a HVAC door opens when you open a car door, and then closes a while after you close the car door. He guessed it might relieve air pressure to make the doors close easier. The PM also has rear flap vents for that. Maybe the dash vent alone isn't enough for a big van.

Anyway, I'm glad to know it's normal, even if I don't quite know why. Thanks for the help.

PS - I'm really glad I installed a hardwired NOCO battery charger that runs off shore power.
 

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I'm hoping what I've read here is what I'm hearing on my brand new 2020 PM 1500 HR 136. Only 120 miles on it and I have been wondering if there is a key-off servo operated blend door opening or closing once in a while, or do I have a squirrel that has moved in to dine on my wiring. The sound sounds like a muffled flutter, or muffled scampering of pitter patter little rodent feet. It is not a scratching or gnawing sound. The sound lasts maybe three seconds and goes away. I'm working on the van interior, so I'm in and out of it all day. Some days I hear the noise like three times during the day. Today it was only once. I've set rat traps, just in case.
 

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It's a device that squirts a colorless and odorless mind control gas into the vehicle.
Gov made it mandatory about 20 yrs ago.
 

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Don’t believe him it’s "fake news", or is it?🤔
 

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You'll never know 'cause your mind is all scrambled from the gas.
And there will be a new crisis on the news tomorrow and you will completely forget we talked about this.
(This message will self destruct)
 

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I'm hoping what I've read here is what I'm hearing on my brand new 2020 PM 1500 HR 136. Only 120 miles on it and I have been wondering if there is a key-off servo operated blend door opening or closing once in a while, or do I have a squirrel that has moved in to dine on my wiring. The sound sounds like a muffled flutter, or muffled scampering of pitter patter little rodent feet. It is not a scratching or gnawing sound. The sound lasts maybe three seconds and goes away. I'm working on the van interior, so I'm in and out of it all day. Some days I hear the noise like three times during the day. Today it was only once. I've set rat traps, just in case.
I am probably non observant of it as I can not recall hearing something out of my normal expectations on my 2018 PM 3500. Once after the van sat for quite some time, the battery did not have enough juice to start the engine (quick fix was just to boost with jumpers & it fired right up).

What I can tell you with a 2009 Jeep that I routinely leave parked for months at an “airside plane tie down” spot that has grass surroundings & not too busy with humans; is I had some marmots get under my hood & chew up some wiring ($150 rewire of engine control wiring). I am unsure of this or what years auto manufacturers allegedly started using an insulation on auto wiring that rodents like to eat as food (unresearched I was told “they” switched to a vegetable oil product or similar). Regardless, the same thing happened on a 2004 1500 Ram I own years ago (parked for a few weeks & in this case I suspect a rat - ya ya pun intended). But I do think it was a rat under the hood.

I think your traps are a good idea, but it is most likely a PM noise from your description and the report of others.
 

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Thanks everyone for the thoughts. Even though mind gas was for me the most likely explanation for a number of issues I've been experiencing lately (could be age related too), I'm going with the consensus that the noise is a normal HVAC function. I can now take the rat traps out of the engine compartment, and now looking on Amazon at gas masks.
 

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My Dodge minivan does this too. It startled me when I heard it the first time when camping in it. I haven't timed it, but I suspect your mind will be further eased if you measure the time between key-off and the start of the noise. I bet it will a consistent interval; like clockwork.

What I still don't know though is what the vent or blender door is doing exactly. For example, if I'm still inside the vehicle, has it sealed off outside air? Or has it done the opposite, i.e. if I had set it to recirculate, does it open up ventilation?
 

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My Dodge minivan does this too. It startled me when I heard it the first time when camping in it. I haven't timed it, but I suspect your mind will be further eased if you measure the time between key-off and the start of the noise. I bet it will a consistent interval; like clockwork.

What I still don't know though is what the vent or blender door is doing exactly. For example, if I'm still inside the vehicle, has it sealed off outside air? Or has it done the opposite, i.e. if I had set it to recirculate, does it open up ventilation?
Good idea to time it for the interval after turning the key to off. However, the van can sit for one or several day, I'll open a door and start doing things, and I'll hear the noise. Now, maybe that means I should time the interval after opening a door. Or is it a temperature sensor activating a blend door? Such a mystery, but since I'm no longer thinking furry gnawing things, I'm not losing any sleep over it.
 

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My last 2 pickups did this. 5-10 sec after shutting down, you can hear a vent flap close. So, I knew it was the same thing in the van.
An off the top guess would be that it closes by default when the vehicle is off. I know that my trucks were almost always in the outside air/non recirc mode. So, if it made a noise, it was probably closing. Same with the van. But I would have to mess with it and really pay attention to know for sure. Which I will probably waste a half hour doing later instead of actually working on the van because this thread had to put this worm in my brain.
Thanks a lot.
 

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My last 2 pickups did this. 5-10 sec after shutting down, you can hear a vent flap close. So, I knew it was the same thing in the van.
An off the top guess would be that it closes by default when the vehicle is off. I know that my trucks were almost always in the outside air/non recirc mode. So, if it made a noise, it was probably closing. Same with the van. But I would have to mess with it and really pay attention to know for sure. Which I will probably waste a half hour doing later instead of actually working on the van because this thread had to put this worm in my brain.
Thanks a lot.
Blend doors operating at some given interval after the key is turned off has been a common thing on most of the vehicles I've owned over the years. But when this van sits unoperated for several days, then without any change in key position, something under the dash operates automatically, that got my attention.
 
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