Separate sound, actually not all that loud on my 350. However I do want to sort the problem otherwise neither I nor my neighbours will bother looking out the window when it goes off. It's just an unlock on the fob to disable, again on my 350 vs. 370.
Have unplugged the bonnet switch so we'll see if it makes any difference. The bonnet is actually a little looser than I would prefer so this might play into the same theory, as does the changing the battery (having simply opened the bonnet).
Cheers,
Jon