The problem is not the issue of driving with the seat belt unplugged but stopping the car and removing the belt when parked. The noise is very loud and grating and will only stop when key is out of ignition.
It is surprising how often you find yourself parked up but need the ignition on for something. :-)
A far better explanation of the problem than mine!
Unfortunately I seem to have given the idea I wanted to drive the car without fastening the seat belt.
Worthers +8