It can be done but only by wiring your stereo a little differently. The way your stereo is wired up at the moment you have a red and a yellow wire round the back - both for power and wired separately (the yellow is live all the time, whereas the red is only live when you have the car's ignition on). The advantage of having a car where you can wire up this way is that when you leave the car and remove the keys from the ignition, your radio is automatically switched off (but this is why you have the alarm tone too).
If you remove the unit from your dashboard and look for the red and yellow wires at the back you will notice that along the yellow wire is a connector that can accommodate two wires (where only one is being used at the moment. There is a similar connector, but for only one wire along the red wire too. If you pull apart the red wire at the rubbery connector and then connect the red wire from the stereo into the spare position in the yellow wire (as is diagram 'c' below) then this will resolve the bleeping issue. However - there is a disadvantage. The unit is permanently supplied with power from the car battery, so each time you leave the car you have to remember to turn your stereo off. This might seem obvious, but if you had the volume turned down then it is possible to forget and you might suffer a flat battery.
Incidentally, the reason the facility to wire the unit like this is provided is that some cars don't provide a separate 'accessory' supply for the red wire to be connected to, so you have no choice.