Enable/disable SMS sent sound?

[PogoStick]

I was wondering if anyone knew how do enable/disable the SMS sent sound that plays along with SMS sent pop-up box when you send text messages. I know most people don't like the pop-up/sound, but I'm trying to re-enable the sound because it has stopped playing. Now when I send a text message, I just get the pop-up box saying SMS sent with no sound. I didn't add/remove/change anything on my phone, so I have no idea why the sound would stop playing all of a sudden, but if anyone knows what I can do, I'd appreciate your input. Thanks.