Loose Forend.

[Pa SxS]

Make sure the 3 screws on the underside of the forend iron are tight. If they are loose, there will be a gap between the barrel and the end of the forend. Chad and Dave, this may solve your problem.

[Autumn Daze]

Thanks Chuck, But I check them regularly. If they become loose the forend develops those nasty little cracks where the wood contacts the iron.