Resolved! STM32L031 noisy, even in reset - EDIT: it's not the STM32
EDIT: it's not the STM32, see latest postHeyho,I have some custom miniature PCBs here, the unholy combination of a super-high-impedance-low-noise amplifier (going to a low noise audio input with 24bit ADC, spectra below from that one) and a STM32L031...