I also owned a Torii IV and while it wasn’t the quietest tuber I’ve owned there was more “noise” going on than say my
ST35 or QS Horn Monos both of which are dead silent through LS and Jubilees. But there was no overt hum as you are describing.
The absolute forest of tubes on the Torii and enough background noise to annoy me led to selling it. Idontknow is right about the
Kenny Russell ST35 though, it is an exceptionally nice piece.