Annoying noise output from DAC0 / A0 Arduino MKR Zero

Community General Discussion
1

Hello everyone.
I write on the forum (hoping for some kind soul) so as to find an answer.

I've finally finished my sketch for audio playback with Arduino MKR Zero.
Quite working as I want but with the only flaw ....... have output on pin DAC0 / A0 an annoying noise (which by the way is greatly amplified by the amplifier 3W attached to it).

I wanted to know if any of you, has the possibility to explain (and possibly advise) the reason of this pin there is a noise of this type, either with the waiting instruction card and is at the end of the audio playback.

Does anyone know kindly explain and / or give me suggestions to eliminate this problem?
I leave you in the description under the program I compiled and running for audio playback with consent by PULLUP button.

#include <SD.h>
#include <SPI.h>
#include <AudioZero.h>

int buttonPin = 1;

void setup()
{
  // debug output a 115200 baud
  Serial.begin(115200);

  // setup SD card
  Serial.print("Inizializzazione SD card...");
  if (!SD.begin()) 
  {
    Serial.println(" fallita!");
    while(true);
  }
  Serial.println(" successo.");

  // 44100kHz stereo => 88200 frequenza di campionamento
  AudioZero.begin(2*44100);

  pinMode(buttonPin, INPUT_PULLUP);
}

void loop()
{
  int count = 0;
  int valuno = digitalRead(buttonPin);
  if (valuno == LOW)
  {
    // Apri file wav da SD card
    File myFile = SD.open("darth.wav");
    if (!myFile) 
    {
      // se il file non si apre, stampare un errore e interrompere
      Serial.println("errore nell'apertura di darth.wav");
      while (true);
    }

    Serial.print("In Riproduzione");
  
    // fino a quando il file non è finito 
    AudioZero.play(myFile);

    Serial.println("Fine del file. Grazie per l'ascolto!");
    while (true) ;
  }
}