does anybody know how to turn off the clicking sound on an 2.5i impreza?

when you lock/unlock your car

You're hearing the relays.

There's no way to make them stop clicking, unless you unplug the battery.

Unless you are able to swap the electrical components to lock/unlock the doors, there is no other way to silence the clicking sound.
I know someone who owns a Hynday Sonata and when locking/unlocking the doors, the click is hardly heard.