It's normal for the microphone to whistle slightly when it is just started. When the device is just started, it needs to learn to adapt to the live sound field environment, and it will stop automatically after the learning is completed.

a) Check whether the indicator light at the microphone cover is on. If it is not on, it means that it is not activated. You need to check the power supply line. If the red light is on, it means that the microphone is in the state of stopping the amplification at this time, and the remote control can be used to start the amplification;
b) If there is no sound when the indicator light is in the green amplification state, first confirm whether the speaker is powered on and the volume is turned on;
c) If there is no problem with the microphone and the speaker, check whether there is any error in the wiring of the audio output line. If the line is not wrong, unplug the 3.5mm audio cable from the microphone, connect it to the mobile phone to play sound, and check whether the line is normal;
d) If the above steps are all correct, you can replace the microphone and test again.