Well thats just wrong in many ways... Don't know why you put brackets around that.
This is all you need to play the sound on the trigger.
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radio_trigger playsound("radio1");
So just remove those brackets and you should be good to go. As a note, brackets are used only with a function, if/else statement, while/do while/for loop, and switch case. There are some others but those are your basics and should only be needed.
http://ugx-mods.com/forum/index.php?topic=2843.0 Well that ^^ plays the sound for all players but you can easily change that by removing the players at the playsound and add the trigger to play the sound.
Edit: if you want to have it to play at the trigger then use this.