My Due makes annoying audible noise when board is powered from USB or 5V pin directly from PSU. Noise goes away when powered form Vin pin by 12V from PSU. Tried to use USB power from battery bank instead of powering USB from my laptop, but it doesn't seem to make a difference.
I have located that the source of the noise is coming from the area next to DC jack. Probing around this area with oscilloscope I found that there is a 3.1kHz ripple (about 100mV amplitude) across 47u electrolytic capacitor (PC1 in the schematic). When I press reset button, both ripple and noise seem to go away. Also tested another Due board which doesn't make this noise, and there is no ripple on it across PC1.
Does anyone know or have any thoughts about what might be causing this? I have included screenshots of the schematic and oscilloscope trace.