Regarding the echo problem with the S7:
I haven’t been able to test it extensively yet, but I just tested one of the suggested solutions from this video “How to fix echo problem on your Samsung Galaxy S8,S7,S6”.
At least with one device with which the echo problem occurred so far, I then tested it and the echo then no longer occurred.
I activated the option “Mono audio” in the settings, as suggested there.
The other advice suggested there is to boot into safe mode once and then boot normally again.
I can’t say yet whether this helps permanently, but have these methods also been tested or has anyone tried them?