s40 buzzing under battery when turned off

alarm 

well the alarm siren is under your battery ,so that will be your fault. first try locking it using the key cos this will then avoid activating the alarm,when you use the remote it automatically activates the alarm and shows up any problem ,and will eventually flatten the battery when you get the time replace the sealed battery in the alarm unit under the battery. hope this helps you squire and g`day!!!!

Ok, but it seems more like a mechanical ticking 

I really fast mechanical ticking. I dunno though.