It's never made sound in SMP. Sorry I have not even done SMP testing but I know in fact you never got it worked. It only plays discs or at least last time in last 1.4.7..
When I made one it just kept repeating that hideous song, "13." Even if I removed the Sonictron, it would continue to play the song. I would have to restart my client to get rid of it, lol. I also crafted it with 13 I don't know if that has anything to do with it.
Edit: Oh yea, I also discovered a bug on how to dupe things with factorization, (critical! SpwnX knows what I'm talking about) and since you're a mod developer, I'm sure you know how/where to contact him. Do you know where I could contact whoever made factorization?