I was sent to a site where the customer had a beat up cortelco phone, the issue was a extremely loud buzzing sound (not static, with faint dial tone. I replaced the phone lines connecting to the base set; no change. I replaced the base set; still no change. And I replaced the old 1 port jack, with a new one; nada. I decided to isolate the wires from the customers side and then got a semi-clear signal (light buzz) facing the providers demark. When I reconnected the sound came back. I repunched all connections, still; no change. I check the line no open shorts detected (will try another toner next time to make sure). So I am stumped what could be the issue? What did a miss?
