int SPK = 0, LO = 110, HI = 1760;
void setup() {
  pinMode(SPK, OUTPUT);
}

void loop() {
  int rnd = random(LO, HI); // delay for tones
  for (int i = 0; i < 20; i++) { // squarewave
    digitalWrite(SPK, HIGH);
    delayMicroseconds(rnd);
    digitalWrite(SPK, LOW);
    delayMicroseconds(rnd);
  }
}