Sorry if this is the wrong forum, I just recently registered with asking this question as motive.
There's a sound that is associated either with sinking or diving, or possibly just watercraft in general. It's at the very end of the Silent Hunter 4 trailer, that sort of ticking sound. I've heard it there, and I know I've heard it elsewhere (Probably U-571, Das Boot or Red October). That eerie sound, combined with the silence of the ocean, just makes me think "Wow, that sound is wicked creepy, I wonder what it is?"
What is it?