loud squeeling noise at 3000 RPM

I purchased an 88 GXL with around 150,000 miles last year.  The car is pretty clean and runs well but I have noticed lately a squeeling noise at around 3000 rpm to go with the rattling noise coming from what I consider to be a very loose shifter.  The rattle occurs when I push the gas peddle down more than a quarter of the way and gets worse the more I push down.  I have been told the rattle may be coming from the heat shield or cat.  Also, I gave the car a tune up last year and this year I had to replace the spark plugs again and now the car idles at 1500 rpm.  I am starting to see a pattern here. ha ha. I dont know much about these cars, any help would be greatly appreciated.  Thanx.

i had this problem with my 82 let me know what it is