I have an annoying small exhaust leak from cold which goes after a couple of mins driving. It happens even when the car is warm and you start it up and drive away. The manifold to turbo gasket, turbo to cat and cat to downpipe gaskets are all new and the downpipe is new. I've checked the turbo to manifold bolts are tight. What can it be ? Is there a fair chance the manifold gasket has gone or the manifold nuts are loose ? Can't think of anything else. This all came about after removing the turno to put a new actuator on.