Quoted from Pinballomatic:Drop target switch. Game can’t clear it so pops the target repeatedly trying to clear it. Check switch it is out of adjustment or loose.
Just set up my new to me ECLE and I'm having the same issue. The constant "shoot the castle" only happens when the drop target is down. Also getting the clicking noise at the drop target as OP mentioned. The target itself feels like its in there solid. What should I be checking for?