Re: How to decrease the buzz noise of the circuit board?

If you are only using "big" ceramic caps to suppress RF current, that ARE YOUR problem.. When we made 1GHz transceivers, the optimum lowest ESR cap 15 yrs ago was < 100pF. Your 22uF caps are behaving big resonant inductors> 1GHz, unless technology has changed significantly. Please verify the SRF of all parts in question.

It looks quite interesting. I guess you have tried to bypass the DC/DC or even the big capacitors and power the board externally but the sound remains unchanged.Is the board soldered or connected to some mother board? The small board should be resonating. I noticed that the board is quite hot. Is it possible that there are some conversion from heat to sound rather than from current to force to sound?

Hi, thanks all of you for your great help.
I have found the source of the problem. GE and SunnySkyguy are really right. That's the inductor problem, and that's also the big current sink.
Hi, I am very grateful for your help.

Saturation losses are too high.. Choose lower ET prouct. or get an inductor with lower losses, pref torroidal.