Starter-Flywheel

• Replace the starter. Sometimes, if the starter motor is grinding the gears on the flywheel, the engine will have a metallic grating sound when you first crank it, although it may not happen every time you turn the vehicle on. Trace the positive battery cable, which splits and leads to the starter and to the alternator. Disconnect the negative battery cable from your vehicle. Remove the starter mounting bolts and the electrical connection leading up to it. Unscrew the copper bolt attaching the positive battery cable to the starter. Replace the old starter with a new one. If the sound continues, then you may need to replace the flywheel, which is much more complex and labor intensive.
  
  

Power Steering

• Check the power steering fluid in your vehicle. If the power steering fluid is low, then it can create a grinding noise whenever the car's steering is being turned one way or the other. Refill the power steering fluid and continue to check it on a regular basis. If there is a leak, then you may need to replace your power steering pump. If your power steering fluid is extremely low, then it is advisable to not drive the vehicle until the fluid is refilled.
  
  

Manual Transmissions

• Drive your car and listen for your vehicle to make a grinding sound when it is put in to gear if you have a manual transmission. If a grinding sound is produced when a gear is selected, then the clutch may be malfunctioning. Take your vehicle to a professionally certified mechanic in order to have your clutch operation inspected and repaired.
  
  

Engine Mounts

• Listen for grating and grinding sounds when your car engine is running but stationary. If your engine and transmission mounts have failed, then your vehicle will make a loud chattering sounds that could also present as metal on metal grinding, especially if the rubber mounts are separated from the metal mounting components of the engine mounts.