Strange crunchy noise when there is any sound on the first line of a daughter board. It's clean when there is no any sound from remote party. Internal extension hears the noise but external doesn't. I can hear it from any extension when select the line directly. Swapped two lines but problem still on the same port. Tested all other ports, any issues. Replaced both analog boards including the main embedded ASU. Didn't help. Any alarms or warnings.
Ideas would be appreciated.
Ideas would be appreciated.