It can be a little tricky to get the Android version of Beat Hazard to find your music, so here's a few tips that should help.
Quick Note: Sound Stalling on Samsung S3?
Go to settings->sounds and turn off 'Auto Haptic'. This will fix the problem
How it works - Android Media Scanner
The Android OS keeps a list of media on your device. The game uses this list to find your music. Because of the scanner, it shouldn't matter where you put your music files, internal or external.
However, sometimes the media scanner list can be out of date or disabled. There are a few ways to fix this in the list below.
The game will read mp3, flac, aac, m4a, and iTunes files. At the moment it won't work with .wma files.
The game cannot read files that have non-English characters
You should be able to put your music anywhere, however, the game cannot read music that is in folders with non-English characters. Note: For phones using Italian, I think the default music folder is /mnt/sdcard/Música/ (The 'ú' might cause a problem which can be fixed by renaming to folder)
Un-mount & Re-mount SD card
If you have an SD card, the first thing to try is to got to settings->storage and un-mount and re-mount your SD card. Re-boot your device and then re-start the game.
Media Re-scanner app
You can download an app that will start the Android Media Scanner, download it here "Rescan Media App". Re-boot your device, run this app and then run the game.
Clearing Your Cache
Cached data also seems to cause problems with finding new music. You can download a cache clearing app here 'Quick Cleaner'. Use this and re-boot your device and run the game.
I've had reports that the PowerAmp app can disable the media scanner. Please check this and it might solve your problem. I'm guessing there are other music app out there that might cause the same problem.
Files from Google Music cannot be played, even if you've downloaded them locally. The reason is that Google haven't yet released an API to allow developers to read these files. Hopefully they will release and API at some point.
If non of these tips helps you out, feel free to contact me here and I'll do my best to help. Unfortunately all Android devices seem to behave slightly differently so a certain amount of experimentation can be required.
If you find a solution not detailed here, please let me know and I'll update this page.