If it is only happening when eating I think it is that she is either happy with her food or she could be grinding up something with her teeth before eating.
My Luna did something that I think sounds a bit similar - check out the noise around 41 secs.
She was not ill when doing this, just a happy hamster.
https://www.youtube.com/watch?v=oQ5i...0UhM6k&index=3