Ok so actually, I just found out that the mp3 files i copied to the device and used as system sounds seem to have a low volume. The stock SFOS notification sounds are loud. But the keyboard feedback sound can barely be heard.
android apps also arent really loud. Eg playing music on spotify is rather low volume.
its a bit weird …
[edit] Maybe the volume on android should be increased? How can this be done? On the XA2 I had aliendalvik control installed, but its not available on the 10ii.