We have a 2 line phone system (Only on line 2) if we don't answer the phone before the 4th. ring callers get a fax tone when they call. sometimes they will even get it on the first ring. We have unplugged the fax machine and callers still get the same sound so it is not really from the fax machine it just sounds that way. I have had a repair person come in and the problem will resolve for a little while but not for long.