I am having a problem were a call that includes two people on CO lines and an extension the two CO callers can not hear each other. I have to repeat everything the external caller says so the other external caller can hear what the questions/answers were. I can hear both parties fine and both parties can here me fine they just cant hear each other. I saw program 990 field 3 for CO volume but I cant tell if this will increase or lower the volume and -3 db doesn't seem like it would make much difference. Any suggestions? This happens on ALL conference calls with 1 internal and 2 external parties.