Customer with over 50 analog ports and no voicemail reports recently, that some phones are ringing just once about every hour. These phones are in hotel rooms so this is a problem at night. I can see, while looking at the "busy" display, that each port incrementally shows busy for a couple of seconds then clears. It will show extension 216 busy, clear; then 217 will show busy, then clear. I am not sure if that is related to the single ring burst issue. They first said it was one room, but have added more rooms to the list. Thoughts?