Corry,
That noise is still a misery to me. It is very interesting that it just started happening after you re-soldered the microcontroller pins. This gives me an idea…I know in other high frequency circuits that i’ve worked with this type of issue has been caused by flux (from the solder) on the board. At high frequencies flux can actually be inductive. So i’m wondering if something like that is happening here. The Quaverato is only operating a 16MHz, so that’s not too fast but it may be fast enough for whatever flux you are using to be inductive. Clean off all the flux on your PCB around the microcontroller and the crystal (and associated components). I make my own flux cleaner by mixing equal parts acetone (you can use fingernail polish remover) and rubbing alcohol. I use a q-tip to clean it off.
This flux idea just came to me, so i have no idea if it’s related to the issue, but i hope so. The other times i’ve seen this issue, for some reason using linear power supplies has helped. Using a battery to test if the issue is power supply related is also helpful.
I’m sorry for the trouble. Let me know if you have any luck after removing the flux.
-Brach