@Sleep mode zZ, I'm hoping you didn't interpret my reply as being directed to you as a way saying that the noise doesn't exist. I don't have the Fuze+ but my other sandisk players have a distinct hiss when playing silence files if the volume is high enough. That's true in both Rockbox and the OF.
I usually use full size cans and none of my IEMs are particularly sensitive so it doesn't bother me. I also have older ears so I don't tend to hear hiss as much as some people. One of the few benefits of reaching middle age.