I have been troubleshooting this one for awhile. When customers are on calls, they periodically hear a "clicking" sound. I have heard it as well, and it honestly sounds like you are on a call and someone clips on with their butt set. There are 24 lines in the system, and it is not exclusive to any trunk cards or even station modules. I renamed all the lines and had the customer keep a log of what lines they were on when they heard the clicking. It is all over the board. Any ideas/known issues?? Thanks in advance.