Truck exhaust sounds tinny when accelerating?

I have a 97 f250 5.8l that i just had the cat taken off of and a new muffler and pipe put on from the headers back and i notice when i accelerate hard or even normal when its cold, it just sounds very tinny almost like a lawn mower. I know it has a new manifold gasket and unfortunately its in the shop right now with a blown head gasket. So could that have been my problem or is it something else?