This just happened to me and I sent an email to my dealer about it already, but I wanted to see if anyone might have some idea or have experienced it before. I'm just going to copy the email I sent as it's pretty detailed, but somewhat long. I'll had a tl;dr at the end though.
Originally Posted by My Email to dealership
I experienced my first non-cosmetic issue today when leaving for work. When I left my house I hit the unlock button on my key and I heard the door unlock as it should. Less than a second later, the car began giving off a loud rumbling noise and was shaking. On first hearing it, it sounded like the engine had cranked and was chewing something up, but I don't have remote start so that didn't make any sense.
I opened the door and realized that it was the speakers that were making the noise. The closest I could describe it is that the radio had come on (which shouldn't happen until I put the key in after the car being off) and the volume had turned itself up to maximum (at least I assume it was maximum, it was incredibly loud and caused my parents and some neighbors to come see what was happening) but there was no actual music playing, it seemed like it was just playing a rumbling static as loud as it could.
I put the key in the ignition and tried to turn the volume down on both the steering wheel and radio knob, but nothing changed. I pulled the key, got out of the car and was going to open the hood and pull the battery cable, but in the couple of minutes it took from the shaking beginning to thinking about the battery, the sound suddenly stopped. I put the key back in the ignition, cranked the engine, and it started without issue and the radio was at the volume I had left it at when I exited the car yesterday, the first tall mark on the screen, which I think is only about 1/5 or so of the maximum.
I know how difficult this would be to diagnose unless you have heard of it happening before so I don't expect much to be done, but I just wanted to make you aware of the issue and check to see if you might have any idea of what took place in case it happens again.
tl;dr: Unlocked the car, began making an extremely loud rumbling noise and shook. Opened the door and realized it was the speakers making the noise even though the radio wasn't on. It wasn't even playing music, it was just a rumbling static sound. Sound stopped by itself after a couple of minutes, after which the car cranked just fine.