Pre engaged starters tend not to jam. The rapid clicking noise is likely to be the starter solenoid fluttering without engaging the starter gear. First job is the check the battery terminals. First on the battery. Prime suspect is the +ve terminal. Take them off and clean them up. Make sure they are tight. If that doesn't work, next do the earth to chassis connection and the +ve lead to starter solenoid connection. If that doesn't work report back!
