i have a 91 Jetta GL, and there's this really loud rattling noise coming from under the hood at about 2100 rpms. it doesn't always do it, but it also does it when it's not even in gear. i also recently found tiny metal shavings in my engine oil, and i think the rattling/grinding has something to do with it. this just recently started happening. any clues to what might be going on?

 

It sounds like your valve train in breaking due to some sort of malfucntion. Remove valve cover and investigate the valve train.