Engine noise and broken exhaust bolt (updated with pics)

If the bolt is broken off evenly with the outer edge of the manifold, you may not have to remove the manifold. Very careful drilling and an EZ-Out should remove the remaining portion of the bolt. The bolt is under no stress right now and should spin easily.

Experience doing this is helpful, but if what you describe is true, it's not a tough job.

Many Good Lucks,
Eric