Here's something I have seen.
The emta was in the computer room sub was experiencing voice drop out, robotic voice, to the people they would call or receive, even on a handset. The emta was moved out into the hallway, same cable, same handset no breakup. The emta was put back in the room, extension phone line to the handset out in the hall and had break up. We ended up moving the emta into the basement at the demark. Sub has not had problem since. Weird