If you’re using the default audio manager, then that’s OpenAL, not FMod. Is that what you’re using?
If that’s the case, then I know exactly what’s happening. It attempts to release the sound data (and free it from memory) when the sound is not playing. That’s both good and bad… it lets you open lots of sound handles and it does the memory management very nicely, but it causes the audible delay problem.
It would not be hard to alter the code for the OpenALAudioManager to fix this problem. We would have to add something like a set_caching method to class AudioSound.