hiss and hum are usually different things. Hiss, especially as you describe it is likely normal. Just the noise floor in your system. If you have to turn your preamp to hi gain to hear it, with no music...then Yogiboy likely has good advice. My guess as to what your hearing is the tremendous gain of your (and most) phono stages. Your other sources cd player tuner don't have to amplify such small signals as your phono stage...
If it's a hum, could be a grounding/ground loop issue. The more hum you get out the better.