Rattling noise....?

I have a 97 Ram 1500 and when i just barely hit the gas like just barely under 1000 RPM i hear a queit little rattle that almost sounds like its coming from the cat or somewhere in the exhaust. Is this just my cat starting to fall apart or something else since it is only at that RPM? Once in a while it wont do it at all. I notice it mostly when the truck has been sitting for a while. Not running..

Could be a noise from the cats, have a friend listen for the source for you.

get under there and shake your exhaust, if you hear nothing, tap on your cat with a rubber mallet. sounds like your cat guts are getting loose.