Speaker Hiss

Recently purchased a Graham Slee Elevator to go with my Slee Phono. Mounted a Dynavector 17D3 mc, .3mv output. Speakers are Tannoy CPA15 Monitors, sensitivity 100db @1 m. I am getting a hissing sound when music is not playing which sounds just like tube whoosh (except my amp is SS). Cannot hear it when the music is on... buuuut, you all know how it is.

Anyone have any ideas as to what might be causing this?