Audio being fed back into the circuit, beeping
U8 has a feedback resistor, but no series resistor between the - input and the microphone.  

With that setup, U8 just amplifies the microphone signal with everything it's got.

Put a 100k resistor in the place of the connection from C17 to R39.  That will reduce the amplification to about 5.

If that's not enough amplification, use a resistor with a lower value than 100k.



This kind of circuit has a natural tendency to develop a feedback squeal.

You amplify the microphone signal, and send it back out through the speaker.

The microphone "hears" what comes out of the speaker, amplifies it again, and again it goes back out of the speaker.  It just keeps getting louder and louder.

You have to turn down the amplification or move the speaker and microphone so that the microphone doesn't "hear" the speaker as well.