I was told that I had an exhaust leak and that it probably just needed to be tightened up. The mechanic went to test where the leak was coming from, but couldn't find it. After taking off the heat shield, they checked to see if it was cracked, which it wasn't. When they went to take the manifold off, there were three bolts that were very loose and had just come out. It was determined at this time that the bolts were broken off. I have had no other previous work done, and was told by the mechanic that the bolts could have been broke off when the truck was put together.