PI3 acoustic emissions

[ACouCam]

Hi all,

We have a project involving the Pi3 as a recording device for some digital microphones.

One side-effect of using the Pi that we noticed is that the electronics itself generate very weak audible and ultrasound. The sound seems to differ in frequency and intensity depending on the load on the power supply of the PI (ex. connecting and disconnecting an USB keyboard, CPU heavy and light load). Just like some SMPS switching the frequency depending on the load. But still any modern SMPS would switch at much higher frequencies than this, so one would imagine that the harmonics would be from X * 100s of KHz upwards. If there isn't of course any other phenomena involved.

See attachment for the spectrum.

Are there anyone else who have noticed this, and someone who could give any suggestion if there is anything one can do about it, other than physically sound insulating the PI.

Kind regards,
Jonas