Wireless motion sensor 5890 PI chiming intermittently

I have an Ademco Vista P-20 panel. The motion sensor is the only wireless part of the system. All doors, etc are wired. The sensor is about 5 years old model 5890 PI. For the last two days an intermittent chime is audible. The keypad says "check zone 13" which is the wireless sensor zone.

I changed the batteries just for the heck of it. Still chimes occasionally. The sensor does set off an alarm when armed. So, the sensor is doing it's job; but, I hear this chime on occasion throughout the day (and I'm sure the night). We don't hear it upstairs.

Any suggestions? At one point I turned off the chime from the keypad but it still chimes.

Any ideas are appreciated.

Wireless motion sensor 5890 PI chiming intermittently