Loud clicking in conferencee calls

I’m running a new installation of FreePBX done from the ISO installer and have an issue. When doing conference calls I’m getting a loud clicking sound once per second with some callers. It’s not there when all users are SIP users, and it’s not always there when POTS line users call in but with some users, it’s there every time they call into the conference. We ALL hear the loud clicking and it’s enough to force us to abandon the call.

It isn’t just one number that causes the problem. We had a 10 person conference yesterday, well, we tried to, but four of the callers, each from a different location on POTS lines, would cause the clicking. We had to give up.

Has anyone else experienced this or does anyone know how to fix this problem? I never had this issue with my Trixbox system. It’s just since the change to FreePBX.

This morning I did the upgrade to to see if that would fix the clicking problem. It did not. The clicking is about twice per second and does not happen with all phones. I did test calls using three cell phones, my desk phone, and two other desk phones calling in from other companies.

With two of us on the phone we had a third person call in and the clicking started. He hung up, and a fourth person called in and the clicking started. The third person hung up and the clicking stopped so we had three of us on the call… no clicking. I had #4 hang up then call back again and the clicking started again! She was on the same phone that a moment earlier was good, but now was making that horrible clicking.

As a result I conclude that the sound doesn’t seem to be related to the person calling into the conference. It’s something in FreePBX that sometimes causes the loud clicking, sometimes not.

How can I identify the cause of this problem when it seems to be an internal cause?

Trying to figure this out… was reading this file. Could this be the cause of my problem? /etc/dahdi/system.conf