More likely than not, it’s your headphone jack. The Fuze comes out from the factory with a very tight receptacle and a lot of people don’t push the male end of the plug in hard enough. (Wow, that’s sounds a little risqué, doesn’t it?) 
Give it an extra firm push to seat the plug into the jack completely. That should solve both your ‘karaoke’ (no vocals) and stuttering problems. The forum is full of posts from new owners experiencing exactly the same issues. 
