Diagnosis
This is almost always caused by having the parent unit's volume turned up too high while using the talk feature. The sound from the parent unit speaker is being picked up by its own microphone and sent back to the camera.
How to Fix It
When you want to use the talk feature, lower the parent unit's volume first. Press and hold the talk button, speak normally into the microphone (usually on the front), release the button. The sound will come from the camera's speaker in the nursery. Keep the parent unit volume low to prevent feedback.
If That Didn't Work
There might be an object placed directly in front of the parent unit's microphone (like a case or a blanket) causing muffled audio that then echoes. Ensure the area around the microphone grill is clear.
Heads Up
The two-way audio on these monitors is half-duplex, meaning it can't send and receive audio at the same time. That's why you hear a delay. It's a system limitation, not a defect. For best results, use it like a walkie-talkie: press, speak, release, listen.