I have a customer that has a 550.4400 and they intermittently have an electrical buzzing sound on the phone. I have swapped phones, replaced station card, used line filters and this noise still returns. The station cable is STP because of RF issues in the area and have moved the port to different cable pairs with no change. There is another extension that is on this cable and it works great....go figure, any ideas.

"Instinctively Telecom"