Buzz suddenly emanating from back of car

Driving 2017 car last week in gas mode when a buzzing sound like interference from the audio system perhaps (but I don’t recall the radio being on) started emanating from the back of the car, possibly more centered on the passenger side but a bit hard to really tell because once I stopped a couple min later I turned the car off and then turned it back on and the sound was gone. Until today when it started again (and I was listening to a podcast via Bluetooth connection) while I was driving. Turning the car off and back on did not change anything nor did turning the audio system off and then back on. Maybe this is related to one of the batteries? Anybody ever experience this?

 

I wish I could tell!

 

Thinking this is NOT something I’m going to be able to troubleshoot on my own - have an appt with dealer next Monday but if the sound isn’t happening then they’ll just shrug their shoulders and tell me to stop by whenever it’s happening again

 

Out driving today with radio off on the highway when the sound started again. It lasted long enough for me to pull over and get in the backseat to investigate a bit further, def not the speaker but more like something in the passenger filter/fan/battery area....it did go away eventually on my way driving back home which makes me think it's not something necessarily stuck in a fan....the mystery continues!