I just found a solution!
Enter the game with the buzz sound and hit Hotkey + A (or 😎 in the joystick. You'll enter the Retroarch menu.
Then I navigated to sound options (main menu>Quick menu>options>samplerate) and changed sample rate to a lower one (44100). I also changed the audio latency (main menu>settings>audio>audio latency) to a lower value (32 ms). Restarted the game and the buzzing / hum sound has dissappeared in ALL games.
Hope it helps.