The #8 cylinder is the closest one to the cat and if the cat were clogged then that cylinder would fill up with burnt exhaust gasses when the exhaust valve opened. not having a good gas/air mixture in the cylinder when the spark plug fires will make that cylinder not fire, meaning that it will mis-fire.
you can get this code reader for 60$ if you get a ride to advance http://shop.advanceautoparts.com/web..._T|GRP2018____
or you can plug "code reader" into ebay and get quite a few results from 20-60$ and if you don't mind waiting about a week (shipping time) then that would be the better bet.
A coffee can is a good place to store home made peanut brittle, and thinking about it, that is what a cat sounds like when the internals have broken loose.

 

lol^

brb goin to make some peanut brittle to see if my plenum's blown

 

The key trick will not work with the newer 2nd generation rams. I think it only worked before '98? I could be wrong, so don't quote me on that.

Does the rattling happen when you rev the truck in neutral? If it rattles in neutral, it's probably the cat. You won't get spark knock (pinging) in neutral.

Is the rattling coming from the engine compartment? Or is it coming from the cat?

Pull the upstream o2 sensor out and see if that helps. If it does, your cat is clogged.

 

They key dance works on both my 98 and 2000.

 

the key trick does not work on my 98 or my dads 99.... it does work on my buddies 01 however

 

I worked on a 97 also a few months back,and it worked on that too. And it works on my 88 Dakota too,lol.

 

doesnt work on my 99 sport...i just went out and tried it...

 

Well I finally pulled the codes and this is what I got:

P0300 - Multiple Misfire
P0305 - Cylinder 4 Misfire
P0305 - Cylinder 5 Misfire

I just had a tuneup done 2 months ago and has run fine since. I was thinking cat, but now this has we wondering if it is a a misfire/bad wire issue. Weird that 2 would go like that. The check engine light just came on yesterday so it must have to do with the issue.

 

Could be injectors or dirt in fuel rail too. You could also unscrew the pre-cat o2 sensor (noisy) but a good indication if the cat is bad.

 

did you figure out what it was??