2019 trunk wind rattle, rear cabin air vents [updated, fix pending]
 

Updated 7/10/2019

video with rattle (watch the whole thing with volume up, its there)
https://youtu.be/uCJFxg31_dY

Scargoes postulated that this is the cabin air vents fluttering in turbulent air

The rattle--it is audible at speeds above 55mph, sounds like a fluttering, gets worse the faster you go, like the more turbulence and wind noise, the worse it gets. It sounds like its coming from outside the body of the car, but its much louder if you drop the rear seat. It is not from the deck lid or the child safety latches. It sounds like a piece of paper flapping in the wind randomly, and slapping against something metallic or perhaps plastic. It goes COMPLETELY away if you turn on the HVAC fan to any setting.

Why is this a problem? Why not just leave the air on all the time? Because if you want to drive with the windows down or even just cracked, at highway speeds, you will hear the rattle. Even if the HVAC fan is on, if the windows are down, no positive air pressure can be generated to keep the flaps from rattling

I did a test drive with my wife driving, and me in the back with the seat folded down, listening. Right away I was able to pinpoint where the sound is coming from. I opened the compartment to the battery and it got very noticeable. There is an equivalent rattle on both sides of the inside of the trunk, coming from the same place on each side. AND, I also confirmed that the sound completely goes away when the HVAC system is turned on to any setting, AC, non AC, fresh, not fresh, doesn't matter. As long as the fans are on and the cabin has positive pressure, the sound is gone.

I now believe this sound is coming from the rear cabin air exhaust vents, of which there are two, one on either side of the car hidden up underneath the rear quarter (see picture in post #13 by mark114, thanks!). These vents are open to the outside and guarded by 2 flaps that are glued at the top. They equalize cabin air with the outside, so that, for example, when you shut the car doors with the windows up, the air has somewhere to go. They allow the HVAC system to operate efficiently, and they also protect your ear drums in the event of an airbag deployment. You can feel them by sticking your hand up and under the body panel overlying it. I believe the flaps are "flapping" closed and shut as turbulent 60+mph air circulates upward under the rear quarter panel. Even a small amount of positive pressure in the cabin props the flaps open and the rattle disappears.

Fix ideas
- snap off the flaps (but what about dirty air, water, road noise, and exhaust gas coming back in?)
- make something to block the turbulent air coming up from underneath (like a cowl?)
- prop the flaps open from the inside
- modify the flaps so they won't flap (scoring with a razor?)
- put something soft around where they are hitting (foam, rubber, etc)
- just remove the whole thing and replace it with a fine mesh screen

Is it when one window is down? If so, have a look here. Interior Whistling Issue...Found the Cause

The dealer tech needs to compare your car to a 'like' vehicle on the lot. If they both do it its either normal or something GM will address at some point. As a GM technician, re-engineering cars is kinda difficult. Try putting masking or painters tape along the edges of the rear glass closing the gaps between the body and glass, including the line along the trunk. See if it changes.

The best thing ive done to track noises which can be deceptive to their originating location is too put a friend in the backseat and take them for a drive and let them pinpoint it. Or put them behind the wheel and you get back there and probe around.

My car is doing the same. I have a 2018 2ss. I only hear it above 50 to 55 or so. Any word on a fix?

It’s the latches for the child seats on the top of the rear seats. Drove me bananas until I figured it out. Also had the dealer stuff some jute under the rear deck lid since that was rubbing also.

Are you sure its the latches? Did you have exactly the same issue, and did turning your hvac system on to fresh air stop the rattle?

I have a similar rattle too in my '18 ss 1le. I've always thought it was something with the trunk and just haven't looked into it deep enough.

I'll take a look at the child seat latches, thanks for the tip!

The HVAC creates positive pressure. Maybe enough to stop it. I don’t hear mine anymore over my MBRP raceback.

OP should just install long tubes and muffler delete. This will make the noise disappear.

If it is a flapping noise like plastic on plastic or rubber on plastic, I'd bet it is the cabin vents behind the rear fascia. Adding a little bit of positive pressure to the cabin will cause enough air flow to keep the flaps from oscillating open and closed.

May be that....

https://www.camaro6.com/forums/attac...2&d=1557303542

There are videos of Camaro trailer hitch installation that show the car with the bumper cover removed.

thats them!! Thanks! I was able to feel it with my hand by reaching up under the rear quarter panel. You can also feel it by reaching down behind the battery on the inside.

I'm going to update my original post to reflect the current status of this issue.

Thanks again, to scargoes for the theory, and mark 114 for the pic. You guys are awesome! This will definitely lead to a fix.

Now, the fix...will take a little bit of creativity. If anybody has ideas...post 'em up!

We must somehow immobilize those flaps so they can't flutter in the turbulent air. Or modify them somehow so they don't catch the turbulent air and flap back and forth.

Add an home made deflector to protect them for the turbulences but still allow them to work to remove the positive pressure...