LM386 module not working
when WTV020 is playing sound, speaker goes completely mute. When it doesn't play sound, little scratchy sounds can be heard from speaker. Maybe it could help with analysis


Indeed - what you are describing sounds like the DC component of the Arduino's output is outside the workable range of the amplifier, effectively cutting it off.  When there is no output, the voltage is within range and little bits of noise are able to be amplified.

You should be able to fix the cutoff problem with a series capacitor to block the DC component of the input, allowing only the AC signal through - a common technique for coupling between stages in Audio and RF systems.

The value of the capacitor will depend on the impedance of the circuit it is driving.  A bare input to many chips could use a quite small value, while a circuit with feedback or a voltage-divider volume control might require a larger or carefully chosen one.