Samsung S3 4.3 update - Cannot change notification sound? My phone is a T branded device. It's got that AWFUL loud and NOISY notification/startup sound. It wakes the dead as well.*  

Back with the 4.1.2 update, I changed it to one of the stock notification sounds, and it was working. Just as you would expect it to be. Now, after the update, even if I set my new notification sound, it won't change. Even settings say I have "Temple bell", but then I get this aaaaawful T-mobile sound.  

[*] When I bought the phone I set up an alarm. The alarm was so loud I almost had a heart attack. Yes, that default sound is that bad. It's terrible.
Thanks to @Shywim's comment, I checked the settings of the Messaging app. Indeed it's got a custom notification sound settings. (You can adjust the settings only if your phone is not muted.)