I think Braro has nailed it. I assume that you are saying there is nothing connected to the phono input at this point? if so, the noise you are hearing is probably a ground issue due to the high gain at the phono input.
To test this, connect a set of IC's to the phono input and switch to the phono setting, you should hear less hiss, but some may still be present without a load on that input.
To test this, connect a set of IC's to the phono input and switch to the phono setting, you should hear less hiss, but some may still be present without a load on that input.