RB951g-2HnD noise (hissing sound) - BUG (software issue)

Hardware MikroTik hardware general
1

Hello, I have RB951G-2HnD and I noticed strange thing - when I loaded the device with some wireless traffic it produced strange sound - like hissing, fizzing etc. I was first thinking it is something about power inductors (maybe cracked and loose one etc) but when I opened the case, the sound was comming from buzzer! What the hell? Some induced crosstalk? Nope - I measured accross the buzzer hard 3.3V and the ripple on 3.3V caused by wireless caused this strange noise!

But why it there 3.3V in idle? I was curious how it changes when it beeps, so I unchecked “silent boot” in system routerboard setting. And the noise stopped! I measured voltage again and there was 0V!

Why the hell is constant 3.3V on speaker when you select “silent boot” in system/routerboard settings?

RoS version (6.23) (latest)
Current firmware:3.19 (latest)

2

Same problem still on 6.33, with silent boot enabled i hear buzzing noise on wireless load.

3

if you exclude sounds buzzer there would be only two options - EMI and fading/dying oxide(electrolytic) capacitors, perhaps.
saw similar on some (past 15-20 ~) rc’s of 6.33 before on some devices, but its coming from buzzer and generally unusual.

4

Most probably it comes from DC/DC converter which works with high frequency.