1990 Jetta mysterious rattle

I own a 1990 volkswagen wolfsburg edition jetta with 193,000 miles on it.
About a year ago when my car would idle at about 1300 rpms and precisely that, it would make a weird rattling noise coming from underneath the car directly under my shifter. After driving from north carolina to florida, it started rattling louder at ALL rpms and it is quite annoying. it doesn't affect the performance, its just extremely loud and i can't figure out what it is. i thought at first it was the heat cage surrounding the exhaust pipe leading out, but i don't think thats what it is. ALSO... my car also has a lot of trouble holding an idle speed at ANY speed.. lately, it's been idling under 600 rpms and struggling very hard to get back up... and when it gets under 600 it makes a scratching noise and until it goes back up above 600. i don't know if it is maybe a clogged fuel system that could be solved with a bottle of fuel system cleaner.. or something else like a fuel filter, (although i replaced that about 3000 miles ago)... any help would be greatly appreciated.

Dale

oh yeah...
i forgot another also very annoying thing its been doing is when i start, a VERY loud belt squeal well, squeals for varied amounts of time and usually goes away when i start moving... what is usually the cause of that?

Check your cat convertor, the core sounds like it came loose. Same thing happened to my "90" typical of the mexican jettas.