Ported knocking on windows

code/game/objects/structures/window.dm

@@ -120,6 +120,12 @@
 		src.density = 0
 		del(src)
 		return
+	else
+		playsound(src.loc, 'Glassknock.ogg', 80, 1)
+		usr.visible_message("[usr.name] knocks on the [src.name].", \
+							"You knock on the [src.name].", \
+							"You hear a knocking sound.")
+		return
 
 /obj/structure/window/attack_paw()
 	if ((HULK in usr.mutations))