I have a new to me 2018 Enclave.. It rides beautifully and is usually no issue except that on random occasions when I get in the car there is a short buzz sound coming out of the vents. It sounds almost like a toy timer, in fact when I first heard it I assumed one of my kids left a toy in the car.. It happens in short 2 second bursts.. It doesn't happen at a regular cadence.. it doesn't appear to be tied to driving a certain speed.. I can hear it on the driver's side primarily but have heard it on the passenger side as well. I've taken the car to 2 dealers and of course no one else can hear it. Does anyone have any idea what this may be? There are no warning lights on in the car.