It is happening on all the phones. I suspect that the problem is either in the wiring or the boards but I admit I am not a phone tech. The phones we are using are new with one exception and I don't think the old one we are using is the problem. The System was wired poorly to begin with and age has caught up with it. My guess is we need to repair the wiring and replace a board. If that can be done with reasonable cost than we should proceed with repair. If the cost gets to high then we should replace the system.