Problem on my truck
 

After installing the cam, etc I started up my truck. I have a exhaust leak coming from my front left header, which I'm not in the mood to fix so I will be taking that to a exhaust shop. But at higher speeds when accelerating my truck for some reason makes a rattling by the exhaust. I don't assume this in anyway would be my cat or anything, would it? It goes away as well when I let off the gas.