On my way home from work yesterday about 2 miles from home, my car started to intermittedly backfire. I popped the hood and found no arching. This morning, I jumped on the freeway only to take it back home as the backfiring continued. Any ideas what it could be? The car has been running fine, the tune-up is fairly recent. I have an exhaust leak somewhere at the manifold if that means anything. Look at my signature for specifics on my set-up. Thanks in advance for your thoughts.