Here's a video of it from last year, but it's sound exactly as it does now.
http://www.youtube.com/watch?v=t9QplGGtRUo
It's really embarrassing once the rpm's hit about 3000. As soon as the car warms up a bit, the noise goes away. Help?

 

Help anybody?

 

Looks like its the stock exhaust, possibly a broken free baffle or tube inside the muffler or resonator.

 

How do I go about fixing that?

 

Looking at your muffler again I realized you have an LX model but it has twin outlets(EX). I take it this is not the original exhaust?

You can't fix the part itself, the cause is usually from the spot welds that held the components together failed. Usually due to rust. If this is the case your only alternative is to replace it. Looking at the video again, it looks like there is a lump at the bottom of your muffler case, and some rust on the right side. Check the muffler case is not fractured, if it is it needs to be replaced now.

However, you can try and pinpoint which component is causing the rattle. Start with the muffler, as its the easiest to remove, turn it on its end and see if anything falls out. Start up the car and rev the engine a bit to see if the rattle is still there, or if anything blows out of the mid pipe.

If your exhaust has been replaced previously by a muffler shop, the connection points may not be in the same area as a factory/factory replacement muffler or mid pipe.

 

It's the original exhaust, I think. Though I'm not sure. Anyway, not to sound dumb, but can I just pull off the muffler? I'd rather not break anything.

 

If it's the original system, there should be a two bolt junction ~ 1' in front of the muffler, after the last 90*. IIRC its before the rear suspension on the passenger side.

 

Alright, thanks. Hopefully I can get outside and try if the weather is good.

 

To ease removal, use PB Blaster or the likes on the fasteners, let them soak. WD40 is a solvent not a lubricant.