What are the symptoms of an exhaust leak at the manifold?

 

A ticking noise that will get louder with increased load.

 

You will eventually see black residue where the leak is, and it will burn the gasket after a while so it cannot seal. Go run your car next to a wall and if you've got a leak you're hear a ticking sound echo off of it. It gets faster as you rev the motor higher, I'm not sure if it will get louder though. It's difficult to hear if you race the motor because you'll drown out the ticking.