is it my choke, or what?

when i warm my car up, and it sits at the 2k range on the tach i've got an annoying as heck rattling problem coming from the left of the car. it only makes noise when the car is first started and the choke kicks in. i'd like to get rid of it. any help appreciated!

btw its an 86 lude

Could be the cat converter, mine did this when backing off the throttle.