Air signal sounds "metallic", "tinny", "hollow", "robotic", "flanged" or "strange"

Symptom: 

The air signal (or even what you hear in the headphones) sounds like what could be described as "metallic", "tinny", "hollow", "robotic", "flanged", or "strange".  Especially when a person is talking on-mic.  

Solution:

This is a feedback problem between the studios.  Regardless of which studio is on the air, Channel 15 in both studios is turned ON and faded up. 

Channel 15 in Studio C plays the audio output of Studio B. 

Channel 15 in Studio B plays the audio output of Studio C. 

Therefore, if Channel 15 is turned ON and faded up in both studios, this creates a feedback loop between the studios, regardless of which studio is on the air.  

What to do:  Turn off Channel 15 on the board.  If you're transferring control from one studio to the other and need Channel 15 "ON" to complete the smooth transfer, then go into the other studio and turn off Channel 15.