High-pitched screeching sounds when making calls and problems with usb-c adapter

Anyone had the same problem? or is in the long to help?

Problems with the speaker and Mrikrophone. There are always high-pitched screeching sounds when making calls. It is especially bad when two faiphone call each other. What can I do to stop this? Without the original case the problem is a little better.

Second problem. In order to use my headphones, I have to connect them to the phone with a USB-C adapter. Listening to music works, but making calls does not. The phone does not recognize the external Mircophone on the headphones. The headphones speakers are recognized. I have tested my adapter and my headphones on another phone and everything worked. What can I do so that it also works on my Fairphone?