It's coming from the unit inside the house . When BB installed it they didn't install the chime connector, I'm wondering if that would solve the problem. It buzzed by itself only when it's cold, but I also hear it whenever the nest senses someone at my door. The buzzing is loud enough I hear it from another room.
One more question. Why did the Best Buy person not install it? I would think they are all trained on these products and know that have to do that. Installing that chime connector is not really optional if you have a chime in your home. Maybe you could get Best Buy to refund all or a portion of what you paid for the install. Or maybe in today's world with Covid it is just worthing letting go and moving on. 😶