Hi
It will be because the radio has been changed from the one that was originally in your van. Because it has not been coded to the van it will bleep all the time when its on. If you have rear parking sensors, pressing the button to silence them will silence the bleeping but only until you switch it back on again. I took mine to a fiat dealer and they tried to re code it but they could not delete the original vans vin from its memory. They told me the only way I could stop it was to buy a new radio and code it to my van. were they telling me porkies, I have no idea but I just left it as it was in the end.