1/ nothing to hear.
2/same
3/same
4/same
grounding everything at the same point didn't change anything.
i tried to output PWM directly from pin11 without using the breadboard and noise remains. so it
seems to not come from the breadboard.
i made a test with another power supply for the arduino and nothing changed (9V battery).
yes LM386 power comes from the arduino 5v.