I don't know what that sound at the 10 second mark was, but the sound at 11 seconds is a POST beep. The POST beep was a single short beep which is indicative of a successful POST. It is possible to have successfully pass POST w/o a display. That said, by "I just built this external build, and it won't work." do you mean that the computer turns on, but there is no display? If so, you could be experiencing an electrical short from one or more components.
For now, ignore the beeps. If you have more than one RAM stick installed, remove all but one, and then try booting up again. If the same beeps and no display issues continue, shut down and move the RAM to another slot. Repeat this until either you have a display, or you've used all of the RAM sticks in all of the slots.
A "no display" concern isn't a normal operation mode, but it is a common problem. I am still quite curious about that first beep I heard from your audio clip. However, display issues are typically related to the following:
1. Bad RAM
2. Bad PSU
3. Bad mobo
4. Bad GPU
Note that some BIOS are designed to use a GPU as primary display. If this is true for your mobo BIOS, then the problem could simply be that there is no GPU installed. You might want to try that as well.
Yes. You'll find that all form factor-specific cases (ATX, BTX, etc) have the same mounting hole patterns. You'll also notice that your mobo will not occupy every hole in the case. This is due to the way the mobos are designed; some are mATX, so naturally, they'll use less space.
I see, thanks. Now I'm pretty much done, except with the most essential part of an internal build - installing the motherboard (which is an LE and not a Pro as I mentioned in my first post). It's a pain in the a** because the I/O shield has clips/tabs which seem to prevent me from putting the ports into the shield..