Hey, this is directed to the web designer. Firstly, cool site! 
However I did notice something was not done properly in regards to the hover-sounds on the menu.
I worked with Google groups and Mozilla groups on implementing a plugin and/or methodology to do this hover-sound effect issue. The issue itself is that when you hover over one of the buttons in the navigation, you’ll notice that the sound file must complete before it will activate on the next hover.
This is fixable by doing the following in javascript and/or jQuery:
$("#navIdOrClass").hover(function(){
sound.play(); //where [I]sound[/I] is a variable that relates the audio element in HTML 5
},
function(){
sound.load(); //This is a new HTML 5 implementation to force-reload the audio element. What this will do is instantly reset the sound once the user's mouse cursor leaves the navigation element. Allowing for instantaneous resetting of the audio element without have to let it finish before it can be played again.
});
All in all, it isn’t really a bug, just something that as a UI-coder/designer I think is extremely easy now with this new methodology in HTML 5 to implement and it prevents users from being confused when they hover over a navigational element.
An example can be displayed on my experimental animation/sound website here:
https://www.TheNextGenWeb.com
^That’s the site im working with Google Groups and Mozilla on to experiment with animations, fullscreen elements, and sound elements in combination. Getting away from Flash. Which, I’m very proud to see that you(the web designer) did. 
This is by no means a form of “advertisement” or whatever, it’s just the only way I have of demonstrating to you(the web designer) what it is that I’m talking about.
I hope this helps!!!
Oh, and Black Mesa: Source is SICK!!! Thumbs up x2 guys, great job.