Sounds like a pipe is split on revving engine

[marky2027]

Got quite a loud "hissing" sound clearly heard when revving the car with the bonnet up. I have read about the vac pipes but this seems to be coming from L hand side of engine bay. My mate who is a mechanic had a quick look when he did my clutch but couldn't see anything. No lack of power and no spanner light. It's a 1.9 150. Are there any common/well known issues that side of the engine bay? It seems to make the noise just on the revs coming down from their peak. Sounds like I've got a boy racer dump valve!!

[jonnybravo]

exhaust manifold gasket?

[marky2027]

exhaust manifold gasket?

Would that throw up a fault/ EML?