Hey,
on my 1986 iroc, there is a strange rattling noise that shows up whenever I let off the gas or at seemingly random times at idle... it will go away after 1-2 seconds. It is very strange and it seems like it is coming from the atcual engine block near the rear of it (Not certain about this). I would compare the sound to... two pieces of metal being scraped together verrrry lightly. Sound is high pitched.

Any help? (ive heard it could be a timing belt)

 

The V8 in your IROC doesn't have a timing belt. I'm thinking the noise is either a broken flexplate or a dry bushing in the distributor. I've seen both but the flexplate cracking is more common. It could even be a loose torque converter bolt that is backing out and brushing against the block, though I wouldn't expect that to be worse at idle. Use a long screwdriver with the handle held against your ear, or a mechanics stethyscope to listen at the dist housing to see if the sound seems to be more clear there. You can dribble some penetrating oil down the shaft of the dist to see if it quits the noise, but be careful not to soak the electronics in it.

The dist shaft bushings are lubricated by engine oil. There are vanes machined into the shaft that pump oil up to the bushings. If the vanes are filled up with sludge,the oiling is interrupted and the bushings dry out.

 

Its hard to tell without actually hearing the noise, but I had a 92 RS that used to make a rattling metallic noise and it was the cat converter heat sheild.

 

My car is also having serious transmission problems if that helps at all. (Slips whenever i floor it or get above 80mph) it just cant upshift when the revs are high.

 

The 700R4, unless it's modified to do so, will not shift into 4th gear above 1/2 throttle. If the trans is slipping in other gears, it needs to be rebuilt. There is a vast array of upgrades to be done to the stock 700R4. It can be built into a neck snapping beast that holds any gear to any speed and holds 4th gear at full throttle above 80mph.