What is the horrible sound?
 

This isn't my Jimmy, but I know you guys on here know a lot more about engines than I do. This is my girlfriends 1999 Grand Cherokee, it has an inline 6, and I have no idea what this sound is, she just sent me this video and I haven't been able to look at it yet. https://www.youtube.com/watch?v=NrHQ...ature=youtu.be

It's kind of hard to tell from that video. It's too far away, and not directed at the vehicle. Check the oil level for starters.