How to disable system sound effect on AlertDialog?

Question

I have an AlertDialog with 2 buttons. I want them to play my custom sound when they're clicked. So I have this code on every button:

SoundUtility.getInstance(Add_Edit_Note.this).playPositive();

SoundUtility is a class I wrote to play custom sounds. Here's the problem: it does play my custom sound, but simultaneously it also plays the system sound effect, so I have two sounds playing at the same time. I was able to disable it on the regular buttons by rewriting the Button:

public class AppButton extends Button {

public AppButton(Context context, AttributeSet attrs) {
    super(context, attrs);
    // Disable sound effect
    this.setSoundEffectsEnabled(false);
}

}

and then in my XML file:

<com.my.app.AppButton
    ... />

but I can't find a way to disable these system sound effects on AlertDialog buttons. Any suggestions?

EDIT

As requested, this is the SoundUtility code:

public class SoundUtility {
private static SoundUtility soundInstance;
private MediaPlayer mpPositive;
private MediaPlayer mpNegative;

public static SoundUtility getInstance(Context context){

    if(soundInstance==null)
    {
        soundInstance = new SoundUtility(context);
    }

    return soundInstance;
}

private SoundUtility (Context context)
{
    mpPositive = MediaPlayer.create(context, R.raw.click_positive);
    mpNegative = MediaPlayer.create(context, R.raw.click_negative);
}

// Playing positive sound
public void playPositive() {
    mpPositive.start();
}

// Playing negative sound
public void playNegative() {
    mpNegative.start();
}

// Releasing MediaPlayer
public void releaseMediaPlayer() {
    mpPositive.release();
    mpNegative.release();
}

}

EDIT 2

The code of my AlertDialog:

AlertDialog.Builder builder = new AlertDialog.Builder(this);
        builder.setMessage("Are you sure you want to cancel?")
        .setCancelable(false) // The dialog is modal, a user must provide an answer
        .setPositiveButton("Yes", new DialogInterface.OnClickListener() {
            // If the answer is Yes
            public void onClick(DialogInterface dialog, int id) {
                ...
                setResult(RESULT_CANCELED); // Setting result as cancelled and returning it to main activity
                SoundUtility.getInstance(Add_Edit_Note.this).playPositive(); // Play positive sound
                Add_Edit_Note.this.finish(); // Closing current activity
            }
        })
        .setNegativeButton("No", new DialogInterface.OnClickListener() {
            // If the answer is No
            public void onClick(DialogInterface dialog, int id) {
                SoundUtility.getInstance(Add_Edit_Note.this).playNegative(); // Play negative sound
                dialog.cancel(); // Closing the confirmation dialog
            }
        });
builder.create().show(); // Present the dialog to the user

Answer 1

Try this

Button btn = dialog.getButton(Dialog.BUTTON_POSITIVE); 
btn.setSoundEffectsEnabled(false);

Call setSoundEffectsEnabled for all the buttons that you have

EDIT:

Instead of

 builder.create().show();

use

AlertDialog dialog = builder.create();
dialog.show();

Button btn = dialog.getButton(Dialog.BUTTON_POSITIVE); 
btn.setSoundEffectsEnabled(false);

Button btn2 = dialog.getButton(Dialog.BUTTON_NEGATIVE); 
btn2.setSoundEffectsEnabled(false);