There are echoes when the signal is sent to the remote terminal through the AUX of the Mixing Console. To clear the echoes, you could follow the solutions below:
1: Confirm the input interfaces of the Mixing Console for remote terminals.
2: Turn on the AUX channels of the input interfaces confirmed right now.
3: Flip on the main AUX control switch of the Mixing Console.
4: Turn off the AUX channel for the remote terminal to the Mixing Console input interfaces
5: To check whether the remote terminal unit turns on the echo cancellation or not.