Quote Originally Posted by PaulStoffregen View Post
Are pins 18 and 19 still showing no voltage?

If so, try measuring the 3.3V power on the bottom right corner behind the headphone jack, of course with the multimeter negative lead touching the USB cable shell or other GND location on Teensy.

No 3.3V reading on SDA and SCL probably means the audio shield isn't getting 3.3V power, because the shield has 2 resistors for those pins which bring both up to 3.3V.
I checked everything, and everything indicates correct voltages!