Carried nodes along to music Rhythm

Hi, I am making the game

that along to the rhythm of music carried rectangulars are coming, remove rectangulars.

but I don't know about how to make the carride rectangulars According to the rythm of music...

How to solve this problem?

I made just randomly carring rectangulars along to music.

void draw() {
rectMode(CENTER);
colorMode(HSB, 360, 100, 100);
println("position : " + song.position()/1000 + "/" + song.length()/1000 + "sec");

fft.forward(song.mix);

stroke(255, 0, 0, 128);
// draw the spectrum as a series of vertical lines
// I multiple the value of getBand by 4
// so that we can see the lines better
for(int i = 0; i < fft.specSize(); i++)
{
line(i, height, i, height - fft.getBand(i)*4);
}

for(int i = 0; i < song.left.size() - 1; i++)
{
line(i, 50 + song.left.get(i)*50, i+1, 50 + song.left.get(i+1)*50);
line(i, 150 + song.right.get(i)*50, i+1, 150 + song.right.get(i+1)*50);
}

stroke(0, 0, 0);
strokeWeight(3);
noFill();
rect(180, 130, 135, 135);
rect(315, 130, 135, 135);
rect(450, 130, 135, 135);
rect(180, 265, 135, 135);
rect(315, 265, 135, 135);
rect(450, 265, 135, 135);
rect(180, 400, 135, 135);
rect(315, 400, 135, 135);
rect(450, 400, 135, 135);

if (start == 1) {
if (s > 135) {
// s = 0;
}
else {
stroke(0, 255, 0);
rect(180, 130, s, s);
s++;
}
if (s2 > 135) {
//s2 = 0;
}
else {
stroke(255, 0, 0);
rect(315, 400, s2, s2);
s2+=2;
}
}

for (int i = 0; i<flashes.length; i++) {
flashes[i].update();
flashes[i].display();
}
Time = millis();
drawRectangle();
}