Those parts/joints look ok.
The issue only starts when the rate knob is lower than 12 o’clock. The rates below 12 o’clock are very slow and barely perceptible as a trem effect, kind of ‘kicks in’ at 12
Since you said the sound was coming through only on the high side of circuit (with calibration mode), it must be responsive to the high trim pot. Are you able to manipulate (lower) the volume level of the noise with that trim pot?
Yeah it’s only affecting the high side of the signal as far as I can tell, if I turn the high pot too high it’ll start making a noise on its own, any lower and it just affects the signal. If I turn it all the way down the issue goes away because the high side of the signal effectively goes away.
This is a very strange issue. It’s strange that it is only happening on the high side, but it could be that both sides are affected the same, but the LPF is filtering out the noise on the low side. The fact that the noise seems to change characteristics with the rate knob makes me think that it has something to do with the microcontroller, although I can’t imagine how it would be behaving this way. If you have a USBTiny programmer, you may consider re-flashing the microcontroller to see if that changes anything. If you happen to own an oscilloscope you can scope the PWMs coming from the microcontroller on each side (high and low) and compare the wave forms.
One more thing I wanted to ask is if it behaves any differently when the mode switch is flipped.
No change with in phase or out of phase, the highs have a trilling sound and the quiet part of the cycle.
Don’t have a scope or a tiny programmer but the retailer is helping me by swapping mine for his built one.
Thanks