Thanks for the suggestions. I found the core of the problem. The audio engine, whatever it is, finds it hard to start. And by the time it's started, the audio is ended. It has nothing to do with the delay setting. If I "testplay" the sound, nothing can be heard. If I have any sound engine open, even from a flash application, the click works.
If noone else has this problem, just ignore me, because probably it's my sound card's driver(xonar dg).
