Hi Jack, please find my comments bellow.
I thought about this issue you face in the night. I think that whilst the PCB layout is probably not optimal due to the small size, it seems most people have no issues.
I created groups.io thread related my issue:
Have to metion I received a few personal messages and part of them contains confirmation of this behaviour.
Moreover one message contains following:
I verified on two Minis here that I hear the clicking when tuning and
when navigating the menus just like you found. I've repaired several minis for people
in the group and they all have the clicking.
I never really thought about it being bad... just a little annoying.
This means for me that problem probabbly common but most peoples do not bothered at all. They play a little and don't care than.
So I theorise that somewhere you have either a defective SMD bypass capacitor or damaged one or bad SMD solder joint. Because the symptoms really seem like a bypassing problem but most people don't have it so probably something already on the board is not doing its job. Not that I can help you find the exact component easily =)
You can check that ROT A and ROT B don't contains any SMD parts on track but just long way through half a board among OpApms.
Forgive me, you might already have shown but I missed, have you traced with the pocket scope the signal path from the output of the receiver through each step until the headphones? It would be interesting to see where the click appears (if it is not present throughout)
I started tracing but get a little bit tired and switches on random debug like bypassing. But I will definitely finish this after some rest.
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