my first guess would be either padding or margin on your li elements. see if this helps:
li {
padding: 0;
margin: 0;
}
(spoke too soon, looks like you do have that in there)
on third glance, it looks like you're setting the following:
ul.menu li a {
display: block
padding: 11px 0 0;
}
see if removing that 11px padding helps