There this annoying rattling this underneath my car, i have had several suggestions that it could be my caty converter, some inside piping(i dunno wut that means) but i would much appreciate honda-tech's opinion. The rattling is getting more constant and im starting to hear it at high speeds as opposed to only hearing it at very low rpm's.

 

Try checking the heat shield around your cat. That would rattle on my gsr at mid rpm.

 

its most likely is the cat converter
my buds DB8 was like that and when we took out the cat converter
the honeycomb inside was broken to pieces, we just broke some more and pour it out and it was fine
BTW it ran alot smooother after that, remember there are 2 section in the cat, we just broke off one side of it not both, if we did that it would be like running on a straight pipe.
hope this help

 

Check the heatshield around your exhaust. If a portion is rotten or has come loose, it will vibrate against your piping and the noise is very annoying, like a tin-ee rattle. Mine only did it at certain RPMS. Just use tin snips and cut the bad portion out. Move onto the cat once you've ruled this out.

Si

 

It is a good possiblity the insides of the cat have rusted out like my old honda or the Heat shield as other have mentioned.

 

Cat. converter heatshield. That's what mine is...I just turn my music up louder

 

two things1)heat shield like everyone else is saying,(2)maybe u could even check your hangers,they could be broken

 

Its the heat shield above the cat, I removed mine on my own, but then your floorboard is going to heat up