I have an issue where we are experiencing a clicking sound on the phones. Im still a newbie at this so please bear with me. Its almost like the sound when someone goes off hook. But it happens every 30 seconds or so. I have ruled out telco by some testing I have done and I have swapped out my combo card for a known good one. The problem is only there during external calls. Extension to extension calls are fine. Could this be some sort of impedance setting I have to adjust or something like that? The problem was more severe with the old combo card, but once I swapped it out it became better but definitely still there. Any help or ideas are greatly appreciated. Thanks in advance.