Strange buzzing noise after installing Sierra

[danny_w]

Hi all! I hope somebody is familiar with this strange issue. I have a 2012 Mac Mini connected via HDMI to a 32" TV that I use as a monitor. After installing Sierra recently (I was on Mavericks), I hear a strange buzzing sound from the Mini whenever I turn on the TV. It usually happens only once for about 1-2s and then quits, rarely it repeats. It is probably nothing to worry about but I never noticed it before and was wondering what it could be.