T3.1 + Audio Board, corrupted sound, possibly soldering issues

[kutu]

that was a noob mistake, i forgot to connect GND pin FailFish

 

[manitou]

As you noted, audio board product page strongly recommends short-wires, or best pins and headers. similar discussion at
https://forum.pjrc.com/threads/41157-Just-noise-with-Teensy-3-6-and-Audio-Adaptor-Board