Noise ADC output and unexpected DC bias in transitory

I'm trying to design a guitar loop pedal with a STM32F411, currently just trying to make sure the input signal is ok. The ADC I'm using is a PCM1808. Main problems are: from the ADC I2S output, I'm getting a weird DC component in the signal right at the moment when I pluck the string. The signal is negatively offset and with time climbs up again to be centered around 0:

https://preview.redd.it/pxtm03zhbyoe1.png?width=1280&format=png&auto=webp&s=ba4b92891e1a8b2fddbe209aea374200918682af

And also all that noise and "ghost" signal (the one that seem to be a weaker duplicate of the original one but with an offset).

As images are limited, here's everything:

Schematics: https://i.postimg.cc/XYwdY2h2/image.png

https://i.postimg.cc/9Xr817rW/image.png

Other samples:

https://i.postimg.cc/vBk5BD7y/Figure-1.png

https://i.postimg.cc/Qx4hW59c/Figure-3.png

Is that normal? I'm unable to plug a DAC at the moment to hear how much this is affecting my signal.