Preamp hissing detectable at low volume?

Is this from your seated postion WHILE LISTENING TO MUSIC?
Or between ?
Or with your ear close to the speakers?

You need to find out which component is causing the hiss. First disconnect the preamp from the amp and short the inputs to the amp with the amp off. Then turn it on. If you hear the hiss, it is in the amp. If you don't, connect the preamp to the amp and short one of the preamp inputs, select this input with the selector. If you hear the hiss, it is in the preamp. If it is quiet, the hiss is in the source.

Next determine if one channel has more hiss than the other, if so, move the tubes across, channel to channel in the offending component. If the hiss changes channels it is one of the tubes that you moved. If it doesn't, you may have a cold solder joint or the like. Some designs are just more noisy than others, but most don't really have much audible hiss at the listening seat with moderate sensitivity speakers.

I change the polarity on things (recently my TT had a little noise after removing it for something...reversed the AC plug and it's quiet again), lift the ground wherever I need to, etc. Even my REL sub that is on a different wall plug than the rest of my stuff had a little noise that I didn't know was there until I put it up to my ear...ground lift fixed that.

Tubes can make a hissing sound sometimes called tube rush. I have a tube preamp and when I put my ear up to my speakers with no music playing I can hear a steady hiss in one channel.

Tubes do have many fine characteristics but they can be noisy. Some can be dead quiet too. I'd swap some tubes if you have extras and see if it affects the noise.

You should be able to buy some very quiet tubes if that is your problem. Some sellers grade their tubes on how quiet they are. Phono stage grade being the most quiet.

Thank you all so much for your responses! This rushing sound is audible from my listening position during idle, and it is evident to me during quiet passages. And thanks for your thoughtful instructions Viridian. I am a little nervous about messing with the tubes in my discontinued SFL3, Special Edition. Can anyone suggest a good outfit for replacement tubes and/or upgrade of other elements within the piece?