Weird. I heard a similar buzzing noise last night while driving - not just when vehicle hold is engaged. I turned off the music and it sounded like it was coming from the front, driver side speaker or something. Not sure if this is the same noise you are experiencing or not. I'm on 2.7.77.
Anyone updated to 7.1 notice that this sound seems to have dissipated dramatically or completely eliminated?
I got updated last night and today I am not hearing the buzzing sound in vehicle hold. I still hear a tiny bit of mettalic sound when I'm rolling to a stop, below 5 mph but once the vehicle is in brake hold, I don't hear it.