My callers always complain about the audio quality when I use my Fairphone in-ear headphones. There always seems to be some kind of squeaking noise. What can I do?
Check out the Public Issue Tracker. There is a bug described as
Distorted microphone audio quality - The microphone produces a metallic, sharp, or hollow sound during calls.
Make sure your earbuds receive firmware updates when they become available.
Open a ticket with official Support.
Could be a fault with the noise cancellation software.