Grinding, metal noise

Welcome to 2CarPros. If there is a noise that is there with the engine running but the vehicle in park so it isn't moving try this test. Have someone watch the engine wile you do this - Put your foot on the brake and hold it down, now put the car in drive, now rev the engine a bit, does the noise get louder? Do the same thing but with the transmission in reverse. What does the noise do? Does the engine move around more than about an inch or two? If it does you likely have at least one bad engine mount. If it stays in place and doesn't move much, shut it off and remove the front drive belt. With the belt off start the engine, is the noise gone? If yes move and spin all of the pulleys and idlers, you are listening and feeling for a loose or rough bearing.
If the noise is still there with the belt off but you don't see the engine moving then look around the transmission/engine bell housing for anything that is damaged, check that the starter isn't binding.

That isn't as bad as some I've seen. Does the noise happen while in motion? Or when do you normally hear it?

A bad idler or tensioner will make noise with just the engine running. It wouldn't need to be in gear or even given any throttle. Your description sounds like a bad mount that lets the engine move enough that something is hitting, either the exhaust or engine.