Rock Star – Home screen menu doesn’t close properly

Hi, I'm using the great, free Rock Star theme. All was fine originally, but now, the Home screen menu doesn't close properly. It is especially evident when the site is viewed on a mobile. It's as if the menu is transparent over the top of the site, but there are lines visible where the divider areas would be between the menu items. The site affected is http://mikefloodmusic.com . How can I correct this, please?