Andy, If you know you have some loose bolts, the obvious thing to do when all is cold is to check and tighten all of them from the exhaust manifold back down to and including the fasteners at the tailpipe. After you do that fire it up and let it come up to operating temp. I hope this is on jack stands at this point. While wearing a real good pair of leather work gloves and a small piece of wood in your hand run it around the donut gasket between the exhaust manifold and exhaust pipe and all other joints and connections in the exhaust system. Don't know if you are aware of how much expansion occurs in that system from cold to operating temperature. But I will go back to my original statement that in almost all instances, a rattle is usually due to some sheet metal contacting something that it shouldn't be, and an exhaust leak will be singing a much different tune
Good luck brother,
Joel