The echo is caused by multiple transmitters online sending the same messages, not quite in sync. As I understand it Andrews has the ability to select any one transmitter (or any and all) in the system if they so desire, and if they did there would be no echo. If they select more than one TX and you have conditions to more than one then you will possibly hear the echo.
Every time I have heard a transmission using the call "Andrews" but seeming to be from a different transmitter it has been preceded by the control tones. I once heard a transmission that was IDing as Andrews with control tones at the beginning and when Andrews unkeyed Offut audio came up in mid word on the same transmitter (in other words Offut had not been under the Andrews TX and the Offut signal levels and audio faults matched the Andrews levels). My assumption is that Andrews had control of the TX and when they dropped it the Offut ops were, and probably had been, trying to use it.
T!
That's what the echo is?
And here I was waiting for them to start talking about their 'lenyears' and turning on 'roger beeps' and hollering for 'big 453 in the sunshine state'. lol.