Actually, those beeps are used to determine if there's any other VRS's turned on in the area. It's part of their algorithm that (in theory) only keeps one radio turned on at a scene. It's SUPPOSED to work like this:
Car 1 arrives, turns on the VRS.
Car 2 arrives, turns on the VRS. Car 1's VRS now turns off.
Car 3 arrives, turns on the VRS. Car 2's VRS now turns off.
Car 3 leaves, turns off the VRS. Car 2's VRS now turns on.
Car 2 leaves, turns off the VRS. Car 1's VRS now turns on.
The idea is that there is always one VRS turned on at any one time within a certain area, and uses "First on, First off", I guess to make it easier?
There's a document on the BMR site somewhere IIRC that explains better how this actually works.