This is probably another stupid question from me, but how do I know if I have a cracked exhaust manifold?

Does it make a similar sound to a leaking muffler?

It's just that my X has started making a strange "farting" sound when the engine is under load. Although it maybe the Gibson SS muffler loosing it's "exhaust quieting down material"?

Any idea's?

Euro' Xterra.

Very hard to describe it in its infancy, not really noticeable unless pointed out by a trained ear. But once it gets a bit beyond that point, it starts to sound a little bit "diesel-like" on cold mornings before it warms up, or at least that's how I'd describe my passenger side last winter. I was informed my driver's side is just starting to go a couple of weeks ago, but he knew exactly what to listen for.

If you can, remove the shield that's bolted on top of the manifold, even if you can't see the crack, if the crack is on the top/outside portion, the shield will show evidence of the leak underneath.

Brent