First off, correct this.
PHP Code:
new const SOUND[] = "sounds/test";
PHP Code:
new const SOUND[] = "test.wav";
Second, you should precache it
And third, what are you exactly trying to do? Do you want to stop the sound at a point?
This might be the answer If I'm not wrong.
PHP Code:
// Add this under client_cmd in event_round_start
set_task(0.5, "function"); // Or any time you think is good enough for your sound
Oh and client_cmd is not supported here, but this looks like a harmless plugin.