Hello,
The noise could come from different sources:
- the microphone
- the connector
- the ADC
- the ADC reading
- in the FPGA if the algorithms are not correct
Depending on the compilation of quartus means that you have noise induces by the power supply, I think.
Do you catch the data from the ADC synchronously without latches? Verify if your compilation warning specify some latches somewhere in your design.
Good luck.
RB