Your baby and parent units may be too close. Move them farther apart. Make sure there is at least 1 to 2 meters between the 2 units to avoid audio feedback.
If the baby unit is too far away it may be out of range, so move the baby unit closer to the parent unit.
Make sure the baby and parent units are not near other electrical equipment, such as a television, computer or cordless/mobile telephone.
Use of other 2.4 GHz products, such as wireless networks (Wi-Fi® routers), Bluetooth® systems, or microwave ovens, may cause interference with this product, so keep the baby monitor away at least 1.5m (5ft) from these types of products, or turn them off if they appear to be causing interference.
If the signal is weak, try moving the Parent and/or Baby Unit to different positions in the rooms.