I have the same issue reported by tobiassej, and just scheduled an appt for next week. When driving over 30mph with the heating on, after several minutes a loud buzzing noise like a rattling bathroom fan starts. Each time the vehicle slows below 30mph to stop, the noise subsides. when the vehicle speeds back up, the noise returns. If while driving with the heat on and the noise present, I shut off the heating, the noise goes away. If I then turn the heat back on, after a minute or less the noise returns. Based on other reading I suspect this is the compressor for the coolant system that cools the batteries, which would presumably be under load when driving over 30mph with the heat on. However it does not make sense that the system would run continuously as it does when driving with the heat on or be that noisy.