White line beneath header on certain pages

I’m at my wits end.

swingshoes.swingouts.dk has a white line under the header image (above menu) on all pages except front page and blog (Nyheder). I suppose that holds the solution but I have no idea what to do.

I have created a child theme for the normal twenty ten theme. What info do you need to help me? What file do you need to see (style.css, header.php, ??)

Any help will be greatly appreciated,
Allan