Microphone on m5go

[zendamage]

Hello everybody.

I just got an m5go, and I'm trying to make the microphone work.
The mic should be in pin G34 according to M5stack's schematic, but when I read from it, it outputs values between 2995 and 3010, and it makes a clicky sound.

This is my code:

from m5stack import *
from machine import *
import os, wave, time


adc = ADC(34)
adc.atten(adc.ATTN_11DB)
lcd.clear()

while True:
    raw = adc.readraw()
    lcd.clear()
    lcd.print( raw, 10, 10)
    time.sleep(0.5)

This is a simplified version of the official M5GO.py

Any ideas what I'm doing wrong?