I would agree, sounds like a typical exhaust leak noise. If you carefully climb under the car while it's running and very carefully feel around the exhaust clamps and joints with your hand, you might be able to locate the exact place the leak is ocurring. Do be careful though, those pipes are extremely hot. Maybe wear a pair of mechanics gloves, they're thin enough that you should still be able to feel the exhaust pressure, and you won't lose any skin if you happen to touch something.

My guess would be the doughnut seal between the exhaust manifold and the downpipe, the joints around the cat, and the joints around the muffler, or the cat or muffler itself. Pipes can also rust through in mid span, at bends and low points where water can lay inside, but I think thats a pretty rare occurrence on modern cars with aluminized or stainless exhaust systems.