SO! I've been meaning to post since for some time (about 19,000 miles ago) but as I now have 21,000 on the clock I figured I may as well start trying to figure out what this noise is!
I've got a 2019 500x with the 1.3, no mechanical issues so far and well taken care of. No accidents, no hard driving, no anything. It's my daily driver here in Columbus Ohio and the terrain is pretty mild as central Ohio is a flat place!
Anyway! This low pitched noise is something I hear maybe once or twice an hour while driving on long trips, but other times randomly but only while on the highway. It does not happen on normal roads, it does not seem to happen under any particular circumstances such as a hill, turn, or under acceleration. It is simply just there for a moment and then it is not. I do not have a recording of if you could imagine the sound that a whale makes on the ocean, that super low pitch HMMMMMMMMMMMMM. That is the sound I am hearing.
Not to nerd out but the closest thing I can think of to compare it to would be from the intro the Lord of the Rings. In the video below, the enemy, Sauron, loses his finger and the "One Ring" kind of explodes. This explosion knocks everyone over and is an extremely low pitch noise that fades out. This is the closest thing I can compare the noise to.
Any input on this would be helpful!
The timestamp for the sound is about 3:44 to 3:47.