Hi there! Completely new to hardware projects, but I've had a friend direct me this way.

The project I'm working on is fairly simple. Our burning man camp has a camp theme song that we play.... over... and over... and over again. So my idea was to make a button that anyone could walk up to and hit, and the song would play through our stereo. It needs a line-in for whatever current music is playing, the audio file stored on the device, a big button, and an output. I set up a Teensy 3.2 with an audio shield, put our song on an SD card and got to work.

My buddy helped me solder everything together, complete with a line-in and an extra WS2812 LED set thing he had lying around. It's been fun putting all of the code together and making it work.

Now when putting it all together, the issue I'm having is that as soon as I turn on even one LED, I get a ton of high pitched noise coming through the line-in. It doesn't happen if I stop the audio passthrough, and doesn't happen if I turn the LED off.

Here's my very basic sample code trying to pinpoint the issue.

Code:
/*
 * A simple hardware test which receives audio from the audio shield
 * Line-In pins and send it to the Line-Out pins and headphone jack.
 *
 * This example code is in the public domain.
 */

#include <Audio.h>
#include <Wire.h>
#include <SPI.h>
#include <SD.h>
#include <SerialFlash.h>
#include <Adafruit_NeoPixel.h>

// GUItool: begin automatically generated code
AudioInputI2S            i2s1;           //xy=200,69
AudioOutputI2S           i2s2;           //xy=365,94
AudioConnection          patchCord1(i2s1, 0, i2s2, 0);
AudioConnection          patchCord2(i2s1, 1, i2s2, 1);
AudioControlSGTL5000     sgtl5000_1;     //xy=302,184
// GUItool: end automatically generated code


const int myInput = AUDIO_INPUT_LINEIN;
//const int myInput = AUDIO_INPUT_MIC;

#define LED_PIN 3

Adafruit_NeoPixel strip = Adafruit_NeoPixel(9, LED_PIN);

void setup() {
  strip.begin();
  strip.show(); // init all pixels to off
  
  // Audio connections require memory to work.  For more
  // detailed information, see the MemoryAndCpuUsage example
  AudioMemory(12);

  // Enable the audio shield, select input, and enable output
  sgtl5000_1.enable();
  sgtl5000_1.inputSelect(myInput);
  sgtl5000_1.volume(.75);
  sgtl5000_1.adcHighPassFilterFreeze();
  // sgtl5000_1.lineInLevel(2);

  strip.setPixelColor(0, 240, 0, 240);
  strip.show();
}

elapsedMillis volmsec=0;

void loop() {
  // every 50 ms, adjust the volume
  if (volmsec > 50) {
    float vol = analogRead(15);
    vol = vol / 1023.0;
    //audioShield.volume(vol); // <-- uncomment if you have the optional
    volmsec = 0;               //     volume pot on your audio shield
  }

  
}

I've tried both NeoPixel and FastLED, and both give me the same issue.

I was hoping for it to passthrough audio, while my big red button slowly breathes with the leds inside of it, tempting someone to come smash it. My friend told me never to output audio while LEDs are going, but that can't be right, can it?

Thanks for any help!
(Quick edit: Should I have posted this in technical support? Don't want to double post so I'll leave it here for now.)