Wow!
Did they have any explanation for your video-captured observations?
I'm sorry to hear that they didn't find anything.
I suggest you learn the location of the air suspension compressor and booster pump fuses and plan to remove the fuses the next time you hear the noise in the video.
The TIPM (fuse box in the engine bay) fuse #F17 air suspension, F22 air suspension control module, F33 brake booster vacuum pump.
Fuse box diagrams (location and assignment of electrical fuses and relays) RAM 1500 / Dodge Ram (2019, 2020, 2021..)
fuse-box.info
Maybe, raise the hood, set the air suspension compressor to run, and jump out to listen if the noise is the same as your video. That would confirm or rule out the suspension compressor as being the source of your grief.
Until you have identified the culprit, I'd be carrying a 10mm wrench and be prepared to remove the negative battery terminal any time you hear that compressor-like noise, after a shutdown.
Another question for clarification, when the video of that noise was recorded, was that with the key off?
I don't believe either of those devices should be running in a key-off state. If they are, we have to question why they're not connected to a switched fuse, meaning they have no power when the key switch is in an off state.
If that noise is only heard with the key off, once we can identify the device and move it to a switched fuse, you should be good to go.
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