I'd suspect very high idle line voltage on the CO line. If it's far enough out from the CO or remote terminal, the capacitive kick when breaking the connection might be enough to cause the system to interpret this as a single incoming ring burst. CO line ports on Panasonic systems are fairly sensitive and will respond to a wide range of voltages.

This will cause the system to engage in the normal ringing timeout cycle, resulting in two or three rings heard on the system phones with no caller ID information displayed.

I've only seen this one time at a B&B out in the country. They were about six miles outside of town and the CO line voltage was boosted to 72 volts. The lines were so hot that they caused squealing when going off-hook and this phantom ring back condition.

We had to beg the telco to switch over to pair gain hardware for the CO lines that appeared on the system. You may need to consider Sandman's loop current attenuators. The fact that this just started happening could easily have something to do with changes in the telco's facilities; something you will never be able to prove.

Ed Vaughn, MBSWWYPBX