I've succesfully ran some code with a teensy 4.1 and an audio shield that takes input sound and outputs it with a delay.
Then, I added MCP23017 expander to my projet and a rotary encoder connected through this expander.
My audio effect still works and the rotary encoder movements are detected but I now hear a continuous low volume and high pitched sound in the background (even if I have no signal on my input). Also, when I turn the encoder, I hear some crakling sound.

I tried to separate the audio shield on SCL/SDA and MCP23017 on SCL1/SDA1 and I still have the same issue.

What can I try to solve that ?
Thank you in advance !