2005 e320 cdi

when I lock the doors a whistle with some crackling noise comes from the drivers side right near the fuse/relay compartment in the engine bay; and the door locks reactivate on their own after about a minute of being unlocked.
The whistle sounds like a car alarm but not loud.
there is no fuse box diagram for the engine compartment fuse/relay box.
Also no codes.
None of my manuals have a diagram either.
Any help would greatly appreciated.

dorje,

Your vehicle has an alarm siren in the rear half of the left front fenderwell. When the siren begins to fail this noise can occur. It could appear to be from the fuse area but it is in the fenderwell. The little chirp chirp is gong scree scree. Replace siren, or ignore.
Additionally if you unlock your vehicle and not open a door the vehicle will re lock after about one minute. This prevents an unlocked vehicle caused by a fumbled key in a pocket or purse. Have a good day.

__________________
Paul