Hey, I have a bunch (40) of sounds set to play randomly for roadkills. Dynamic is set to true, they're being picked randomly, it's all fine.
Although, sometimes the default sound is being played, even though in the Collection Editor, all Members are set to a custom sound effect.
Sounds and vpk for testing:
http://www92.zippyshare.com/v/pAMYKJbD/file.html