exhaust was backfiring/ popping

ok, yesterday my exhaust started popping or backfiring or something.. i just happen to be bored and filming while i was driving.. lol.. just wondering what would cause this.. its towards the end.. not long at all..
video here:
MOV00775-1.flv - Video - Photobucket - Video and Image Hosting

it wasnt completely warmed up yet either, so that could have been it.. it hasnt done it since and hasnt done it in the past

my car pops like that when the exhaust isnt warmed up. it also quiets down as it warms. i think it has to do with the metal expanding and contracting.

yea.. thats what i was thinking.. it just had me trippin out for a second wondering what the hell happened..

are you running a cat?