Let me guess, you're using Lightflow and the stock Touchwiz UI?
There's been a long standing bug in how Lightflow and TW interact. I ran the two together for about a month without issues (on an earlier ROM), and then suddenly the problem started up. There doesn't seem to be any rhyme nor reason to what triggers it. LF says it's a bug in TW, Samsung doesn't say anything. The best way to get rid of it is to use an alternate launcher. I switched to Nova, and decided I like it better than TW anyway.
Another option is to disable Google TTS and Samsung TTS, but if you do that Google Now won't talk to you, and the navi app won't read street names.
There is a trick to navigating the screens when Talkback is on:
Talkback is hard to turn off, because it affects how the system responds to touches. A single tap just reads what it is you're tapping on. To actually tap a button, you need to wait until the phone shuts up, then single tap it to set the focus, and then double tap the button or item you want to tap. In order to scroll a screen, you need to use two fingers.
So you have to wait for it not to be talking, then tap, wait, double tap to select settings, use two fingers to scroll down to Accessibility, tap, wait, double tap Talkback. Tap, wait, double tap the "off" button. Then wait, tap the OK button, wait, and double tap the OK button.
Whew! I think I've got all that right.