It seems more often than not, when I start my car I can smell methane (smeels like rotten eggs) sometimes. Is this an indication of a bad cat?

Yes that could be, do you get a CEL.
eventually the check engine light will go on and thats when its real bad.

buy yes its probably going bad if you smell rotten eggs, or maybe someone taped a fish to your muffler :)

only thing i know of the makes the rotten eggs smell is a bad cat.

yup, your cat is bad if your car smells like it has a test pipe :)

i have the same problem and i think the cat is under it's own 80k warranty or something. anyway, i went to satan to make them replace it and they tried to blame it on everything else, especially the short ram intake(which they thought was CAI, dumbasses). well i ended up leaving real pissed b/c they wanted like an hours labor to "check all the sensors", and then they would be able to determine what it is. i was like freak you, you don't have to manually check all the sensors, you just plug the computer into it, do you think i'm stupid. then they tried to say that that's what they meant and it would still have to be an hours labor. anyway, it still smells but not as bad since i put in some fuel injector cleaner, and some oil additive cleaner. i'm gona find a new dealership to do it sometime, or get a high flow cat eventually.

sounds like a exhaust leak to me... check the bolts leading from your cat to the rest of the exhaust