Signal leakage when volume is turned all the way down
You need to reduce R11 to zero if you expect the volume to go to zero.

If you are hearing distortion, the output may be clipped. Since they put the volume control after the amp, this is a possibility. Do you have a scope?

I don't care for this design. LM386 are designed to drive speakers, so although they will work, they are not the best choice. The output impedance is variable, it depends on the volume setting.