Line left above header image when text switched off

in twenty-eleven, in Appearance > Header, there’s a function “Display Text” which I have switched to “No”.

Except a Grey line remains immediately above the image and is full width

When the text is showing, I can see the grey line at the top of the white text area – it looks like a shadow effect.

Anyone know how to kill this line?

Thanks – https://www.copywriting.id.au