Start Relay

If a starter solenoid receives insufficient power from the battery, it will fail to start the motor, and may produce a rapid clicking sound. The lack of power can be caused by a low battery, by corroded or loose connections in the battery cable, or by a damaged positive (red) cable from the battery. Any of these problems will result in some, but not enough, power being sent to the solenoid, which means that the solenoid will only begin to push the engagement gear, making the metallic click sound.