Machine gun noise under dash, around 10Hz

A month or two ago, my 2017 Prime Plus (aka base/LE trim, purchased new, 132K miles now, never a problem worse than a stuck auto high beam dimmer switch) scared the crap out of me, with a sudden machine gun clicking noise coming from somewhere over toward the shifter or glove box. Pretty loud clicking, pretty fast, lasted a second or two. Then similar happened on some days, not on other days. Then every day, sometimes more than once.

I got pretty good at counting the clicks, or at least thinking I did. The most common scenario is 18 clicks at about 10 per second. Playing the rock opera Tommy (London Symphony Orchestra version) at volume setting 45 does not drown it out.

As time went on, it became less limited to 18 clicks, though seeming to be in bursts that long, maybe with a pause between them, maybe not. A few times now, it has done probably at least 10x or 20 clicks, meaning about 18 seconds of continuous madness happening in the car.

Every Wednesday, I drive my 3.5 year old grandson to his home from another grandparent's house. So, today I will try to pay attention and log what happens, maybe remembering to record the whole ride on a "voice note" on a phone. Maybe then I can confirm the speed and duration of the clicking more accurately.

The most common times for it to do it, are soon (maybe 30 seconds) after turning the car on or turning the car off. But just randomly idling or driving, it will do it.

Based upon Googling and pondering, it seems very likely related to the climate control blend door servo motor or gear teeth. Yet, with the climate control purring along at steady state during an hour-long drive, not having changed anything in many minutes, it will suddenly do it.

Has anyone had this same problem? I found a bunch of references to servo and blend door problems causing people to get blasted with unstoppable heat, but that is not a symptom in my case. The climate control seems to be doing what I set it to do, I'm just getting this machine gun sound from under the dash.

 

I routinely change the cabin air filter, and permanently (I hope) won the battle with the rodents a couple of years ago. Mouseproofing the firewall rodent access highway was a fun project, a whole story of its own. My daughter and I each own a Prime, so we did both cars. Then, because a mouse found a way into the HV battery area under the hatch, we mouseproofed the access to that space also, they were getting in through cabin/battery air exhaust rubber flaps between the trim panels and fender quarter panels.

This noise is MUCH louder than the blower wheel spinning against a stuck acorn, don't ask me how I know. But to answer your question, I haven't checked the cabin air filter since the new noise started.

I've paid more attention to the noise. It is approximately 18 clicks at around 10 per second, then a very short break (missing 2 or 3 clicks maybe) and repeating. Most often, it repeats 14 times. So about 30 seconds of making a lot of noise.

It was reliably doing the 14 bursts, but now sometimes does just one or two, or the last burst might be 3 clicks instead of 18ish. Many variations. I will enlist my able assistant (the Prime owning daughter) to help hunt down the sound while it is happening.

 

No, it is set the same way I've had it set for the whole 133K miles, I don't use any auto modes on the HVAC, the EV/HV mode, or the high beams. I like setting things myself. I am willing to break that general rule by setting the dome light on auto.

I do agree that startup/shutdown procedures trigger the noise. But it will also randomly trigger itself while driving at complete steady state, having changed nothing.

 

My latest update is that it goes through phases of doing it several times per hour then maybe nothing (except at startup and shutdown) for an hour.

Also, it sometimes clicks around 2x as fast, so let's say 36 clicks at 20 per second, versus 18 at 10 per second.
Similarly, it sometimes clicks only about half as fast, say 9 clicks at 5 per second, but this is more rare.

Also, it will do various combinations of that in a given burst, or differences between burst, changing during its set of 14 bursts. Sometimes it is like a fairly creative, syncopated drum solo for a burst or so, before returning to just rapid-fire clicks at constant intervals.

There have been several times when there is no pause between the 14 bursts, just continuous clicking, but this is unusual.

After turning the car off one time, plugging the car in to charge, then opening the car door to hit a steering wheel to do the charge now vs later, it did its clicking routine, but because I was leaning in the passenger door, I heard a little better triangulation on where it is behind the dash, plus heard an additional, much fainter whirring sound as if a blend door was being moved.

One other symptom is that while driving and not hearing it for many minutes, upping the fan speed (manually pushing up the fan speed button) has maybe a 25% chance of instantly triggering it.

I don't relish disassembling stuff under the dash to be able to feel around for it, using my fingers as a stethoscope. When the weather gets reasonable, I guess I'll have to do so. I'll see what I can get at with the glove box removed, first.

Personally, I've adapted to the sound, and am no longer startled or annoyed by it, despite it being VERY loud. Fixing it will be so that I can carry a front seat passenger without needing to apologize in advance for it being sure to scare the crap out of them.