That crack worries me. The noise and the crack may be related. It's hard to be certain without actually looking at the engine.

Other noise sources off the top of my head that may match your description would be:

1. Loose timing belt or drive belt, flapping/vibrating
2. Related to #1, the tiiming cams may be altogether off. This can happen if the timing belt jumped a tooth. This may cause extensive damage, may be the reason for the crack
3. An exhaust leak