I've never noticed this while in the car, but the other day, I wanted to pre-cool the car and fired up the AC from the app. I happened to be near the car as I was puttering around the garage. I noticed that as the AC turned on, there was a fairly loud audible hum as the AC kicked into high. After about 30s it calmed down, but the hum was still audible from the outside. I tested again at a different time and noticed the same noise, climbed in the car and could not hear the hum. I'm just wondering if this is normal sound or if I should be concerned and have it checked out.