Hi and welcome to the forum.
If you still have the default OS and are using default apps to listen to sound I’d say you may well be the only one and it would be wise to contact Fairphone soon as they have quite a slow response sometimes 
They will likey ask you to
a) Start in safe mode, which disbales any apps you installed temporarily
b) Do a factory restet ~ before you do that you will want to back up any personal data
Anthor issue is if you have an SD card remove if before you do the tests and ensure it is formatted as Portable.
https://support.fairphone.com/hc/en-us/articles/4405445311249