4WD with XY-joystick and L293D issue

Alright, it is working! But.... I have an annoying buzzing sound when not moving. Does anyone has a solution for this?

#include <AFMotor.h>

//initial motors pin
AF_DCMotor motor1(1); 
AF_DCMotor motor2(2); 
AF_DCMotor motor3(3);
AF_DCMotor motor4(4);

int motorSpeed1 = 0;
int motorSpeed2 = 0;
int motorSpeed3 = 0;
int motorSpeed4 = 0;

char command;
void setup()
{

  Serial.begin(9600);
  Serial.println("Joystick Test Code");
}

void loop() {

  int xAxis = analogRead(A0); // Read Joysticks X-axis
  int yAxis = analogRead(A1); // Read Joysticks Y-axis
  
  // Y-axis used for forward and backward control
  if (yAxis < 470) {

  int motor1Speed = map(yAxis, 470, 0, 0, 255);
  int motor2Speed = map(yAxis, 470, 0, 0, 255);
  int motor3Speed = map(yAxis, 470, 0, 0, 255);
  int motor4Speed = map(yAxis, 470, 0, 0, 255);
    // Set Motor A backward
  motor1.setSpeed(motor1Speed); //Define maximum velocity
  motor1.run(BACKWARD); //rotate the motor anti-clockwise
  motor2.setSpeed(motor2Speed); //Define maximum velocity
  motor2.run(BACKWARD); //rotate the motor anti-clockwise
  motor3.setSpeed(motor3Speed); //Define maximum velocity
  motor3.run(BACKWARD); //rotate the motor anti-clockwise
  motor4.setSpeed(motor4Speed); //Define maximum velocity
  motor4.run(BACKWARD); //rotate the motor anti-clockwise
  }

    else if (yAxis > 550) {
  int motor1Speed = map(yAxis, 550, 1023, 0, 255);
  int motor2Speed = map(yAxis, 550, 1023, 0, 255);
  int motor3Speed = map(yAxis, 550, 1023, 0, 255);
  int motor4Speed = map(yAxis, 550, 1023, 0, 255);
  
    // Set Motor A forward
  motor1.setSpeed(motor1Speed); //Define maximum velocity
  motor1.run(FORWARD); //rotate the motor anti-clockwise
  motor2.setSpeed(motor2Speed); //Define maximum velocity
  motor2.run(FORWARD); //rotate the motor anti-clockwise
  motor3.setSpeed(motor3Speed); //Define maximum velocity
  motor3.run(FORWARD); //rotate the motor anti-clockwise
  motor4.setSpeed(motor4Speed); //Define maximum velocity
  motor4.run(FORWARD); //rotate the motor anti-clockwise
  }
 if (xAxis < 470) {

  int motor1Speed = map(xAxis, 470, 0, 0, 255);
  int motor2Speed = map(xAxis, 470, 0, 0, 255);
  int motor3Speed = map(xAxis, 470, 0, 0, 255);
  int motor4Speed = map(xAxis, 470, 0, 0, 255);
    // Go Right
  motor1.setSpeed(motor1Speed); //Define maximum velocity
  motor1.run(FORWARD); //rotate the motor anti-clockwise
  motor2.setSpeed(0); //Define maximum velocity
  motor2.run(FORWARD); //rotate the motor anti-clockwise
  motor3.setSpeed(0); //Define maximum velocity
  motor3.run(FORWARD); //rotate the motor anti-clockwise
  motor4.setSpeed(motor4Speed); //Define maximum velocity
  motor4.run(FORWARD); //rotate the motor anti-clockwise
  }

    else if (xAxis > 550) {
  int motor1Speed = map(xAxis, 550, 1023, 0, 255);
  int motor2Speed = map(xAxis, 550, 1023, 0, 255);
  int motor3Speed = map(xAxis, 550, 1023, 0, 255);
  int motor4Speed = map(xAxis, 550, 1023, 0, 255);
  
    // Go left
  motor1.setSpeed(0); //Define maximum velocity
  motor1.run(FORWARD); //rotate the motor anti-clockwise
  motor2.setSpeed(motor2Speed); //Define maximum velocity
  motor2.run(FORWARD); //rotate the motor anti-clockwise
  motor3.setSpeed(motor3Speed); //Define maximum velocity
  motor3.run(FORWARD); //rotate the motor anti-clockwise
  motor4.setSpeed(0); //Define maximum velocity
  motor4.run(FORWARD); //rotate the motor anti-clockwise
  }
  
}