Exhaust manifold/headers leak
So a couple weeks ago I changed out all my brake pads and put new rotors on the front. I was having issues with the front driver caliper seizing up and bought a new caliper to replace it. Long story short I cut my hand really bad doing something else, had to have stitches, and ended up paying my roomate/bestfriend's dad like to 20 bucks to replace the caliper and bleed the brakes. (He is a mechanic)
Anyways while he was doing it he asks me "Do hear that?" and I am like "hear what?" He told me he is pretty sure my exhaust is leaking and then when he got closer to the engine he told me that it is probably the manifold. After the car warmed up the sound went away and he just shrugged it off and said "dang fords", he is a Chevy guy.
So is this something I should be concerned about? Or can I get by for now and replace it later and just redo the whole exhuast. Is it robbing me of any horsepower/fuel economy?