New to DFPlayer (detect when audio clip has finished playing & loud pop upon power on/down)

//import needed libraries
#include "Arduino.h"
#include "SoftwareSerial.h"
#include "DFRobotDFPlayerMini.h"


//project vars
const int buttonPin = 19; //Pin (A5) the pin that the pushbutton is attached to
int buttonState = 0; // current state of the button
int lastButtonState = 1; // previous state of the button
boolean doCompletionCheck = false;

//FSM state control/vars
#define S_IDLE 1
#define S_POWERON 2
#define S_POWERDOWN 3

//FSM init vars
static int state = S_IDLE; // initial state is 1, the "idle" state.

//instantiate class instances
SoftwareSerial mySoftwareSerial(10, 11); // RX, TX (DFPlayer connections)
DFRobotDFPlayerMini myDFPlayer;

void setup() {

  //debug (monitor)
  Serial.begin(115200);

  //talk to DFPlayer
  mySoftwareSerial.begin(9600);

  //declare pin & state
  pinMode(buttonPin, INPUT); // initialize the button pin as a input
  digitalWrite(buttonPin, HIGH); //use interal pull up resistors

  //check on DFPlayer state (ready for use?)
  Serial.println(F("Initializing DFPlayer ... (May take 3~5 seconds)"));
  if (!myDFPlayer.begin(mySoftwareSerial)) {  //Use softwareSerial to communicate with mp3.
    Serial.println(F("Unable to begin:"));
    Serial.println(F("1.Please recheck the connection!"));
    Serial.println(F("2.Please insert the SD card!"));
    while (true); //keep checking,...repeat
  }
  Serial.println(F("DFPlayer Mini online."));

  //why?
  myDFPlayer.setTimeOut(500); //Set serial communictaion time out 500ms

  //----Set volume----
  myDFPlayer.volume(9);  //Set volume value (0~30).
  Serial.print(F("CURRENT VOLUME: ")); //read current volume
  Serial.println(myDFPlayer.readVolume()); //read current volume

  //----Set different EQ----//
  myDFPlayer.EQ(DFPLAYER_EQ_ROCK);

  //----Set source device, we use SD as default----//
  myDFPlayer.outputDevice(DFPLAYER_DEVICE_SD);

  //play boot sound on power-up
  myDFPlayer.play(1);

  Serial.print(F("INTIT STATE: "));
  Serial.println(state);

  //delay to let boot sound play and start 'listening' for interaction
  delay(3000);
}

void loop() {

  //FSM state listener
  switch (state) {
    case S_IDLE:

      //check main button state
      buttonState = digitalRead(buttonPin);

      //** button state HAS changed (compare) **//
      if (buttonState != lastButtonState) {
       
        //-- button state changed and is: pressed (ie: down) --//
        if (buttonState == LOW) {
         
         //any time button is pressed down, trigger power on sound
          state = S_POWERON;

         
        //-- button state changed and is: not pressed (ie: up) --//
        }else {       
             
          //any time button is released, trigger power down sound     
          state = S_POWERDOWN;
                         
        }
       

      //** button state has NOT changed  **//     
      }else{
               
        //check if -still- pressed
        if(buttonState == LOW) {
          //Serial.println(F("READ STATE: "));
          //Serial.println(myDFPlayer.readState());
                   
         if(doCompletionCheck == true){     
            Serial.println(F("watching audio file for completion"));     
           
            //dedicated function attempt for checking track completion
            trackComplete(2, 3, 'l');             
           
            /*
            if(myDFPlayer.readType()==DFPlayerPlayFinished && myDFPlayer.readCurrentFileNumber()==2) { 
              Serial.println(F("audio finished..."));
             
              myDFPlayer.loop(3);
              doCompletionCheck = false;
            }
            */
          }

                                   
        }else{
          //Serial.println(F("BUTTON STILL -NOT- PRESSED........ "));   
        }
      }

      //update/save the current button state for next loop/cycle
      lastButtonState = buttonState;
    break;

    case S_POWERON:
      //play power up     
      myDFPlayer.play(2);     
      doCompletionCheck = true;     
     
      //return to button checking
      state = S_IDLE;
    break;

    case S_POWERDOWN:     
      myDFPlayer.play(4);
     
      //return to button checking
      state = S_IDLE;   
    break;
  }

}

//playMode options: p = play or l = loop
void trackComplete(int currTrack, int newTrack, uint8_t playMode) { 
  Serial.print(F("Current Track that is playing: "));
  Serial.print(myDFPlayer.read());
  Serial.print(F(" / "));
  Serial.println(myDFPlayer.readCurrentFileNumber());
 
  Serial.print(F("Checking for completetion of track: "));
  Serial.println(currTrack);
  Serial.println(F(""));
  Serial.println(F(""));
 
  //if(myDFPlayer.readType() == DFPlayerPlayFinished && myDFPlayer.read() == currTrack) {
  if(myDFPlayer.readType() == DFPlayerPlayFinished && myDFPlayer.readCurrentFileNumber() == currTrack) {
  //if(myDFPlayer.readType() == DFPlayerPlayFinished) {
   
    doCompletionCheck = false;
   
    Serial.print(F("TRACK MATCH: "));
    Serial.print(myDFPlayer.readCurrentFileNumber());
    //vs.
    Serial.print(F(" / "));
    Serial.println(myDFPlayer.read());       
   
    Serial.println(F("Setting completion listener off---->"));
    switch (playMode) {
      case 'p':
        myDFPlayer.play(newTrack);
      break;

      case 'l':
        delay(800);
        myDFPlayer.loop(newTrack);
      break;     
    } 
     
  }
  //back to button checking
  state = S_IDLE;
}