Engine Noise

I just finished a 625 mile road trip over the highway. I averaged fairly high speeds for the duration of this. I returned last night and then this morning on my commute to work I noticed a loud noise from the engine. It sounded similar to an airplane engine at high speeds. What would account for this?

Possible exhaust noise at the manifold or a blown muffler or hole in the exhaust pipe. Possibly a blown head gasket.