I bought a 2.5" Dynomax catback system from some guy.
He said he has used the system for a few years and it's seen very little mileage.
But when I shake the muffler, I can here rattling like there was a fair amount of sand in there..
It's probably rust and corroded metal..?

My question is, should I ditch the muffler or will the debris come out of the muffler when I install it?

 

It's not a Dynomax VT series muffler, is it? The VT has an internal valve. And while it's held by a spring, you might be unseating it when you shake it.

http://www.dynomax.com/mufflers/dynomax-vt-mufflers

Also, from what I have read, early versions of the VT could rattle at idle. Dynomax later added some "padding", or a soft stop, to prevent this rattle.

 

No, I don't think it is.
This is the product:
http://www.summitracing.com/int/part...t/model/camaro

I think that there's just a bunch of corroded metal inside.

 

There's no way I would put a muffler on my car that rattles.

I would get my money back if you can.

If you still have a stock system that's in good condition and just want to change the sound just buy a muffler.

Its either that or upgrade to a complete 3in. system.

Each muffler is going to have their own distinct sound so pick carefully or you may end up hating it.

 

I found out the cause for the rattling! But not a solution..

I shook the muffler in my hands for a good 15 minutes and eventually a few black "rocks" came out from the left outlet. There are still plenty of these left inside and these ones came out by sheer luck.
What could they be? They vary in size and they look like asteroids because they have craters in them, meaning they have burned at some point. Kind of like coal.

Good thing is, theres probably nothing wrong with the muffler and it's not rusty inside. But I still want these rocks out of there. What could I do? I'm thinkin about drilling a hole but I don't want to ruin my muffler.

 

They might just blow out when you start the car.

 

Could be... just to be absolutely sure I could open the whole thing up.

Here's a photo of what came out:

http://i6.aijaa.com/b/00994/13238534.jpg

 

That looks like strata (?sp) from the cat that was ahead of that muffler on the previous car.