I didn't realize that this was even a thing, but googling/reading about it makes perfect sense with what I'm seeing. It definitely sounds like an electric compressor, stops around a minute after engine starting, though it's strange that it doesn't always happen. This morning was colder than it has been lately (~35 degrees), and it did not happen today; where-as last week it was doing this on 60 degree days (granted this difference is trivial compared to cat converter temperatures, but I would imagine that it should kick on during every cold start?)It’s an intentional strategy that runs the secondary air pump and runs the engine rich and at high RPMs to accelerate heating the cats on cold start up. It’s pretty common across many makes/models, but FCA seems to make it especially obnoxious on many vehicles.
Makes me wonder if either there's some complex logic that determines when this pump engages, or if perhaps there might just be an issue with it as to why it's occasionally so loud.
Service appt is set for Thursday, I'll talk to them about it just to be safe.