What's causing hiss??

What Mechans said. Incidentally and apropos of nothing, it's this constant dance of second-guessing and general fussery that sent me - with much wailing and gnashing of teeth - back into the comforting, predictable camp of solid state. Say whatever you like about the sound, tubes are unquestionably higher-maintenance, less predictable, and more like living little bits in their own right, in all of the good and bad connotations that might evoke. Just part of their care and feeding to grow accustomed to, although once you get the right ones in a preamp section, you can usually forget about them for a couple years. Unless, of course, you can't.... ;)

Is the hiss audible at your listening position or just when you put your ear up to the speakers? Assuming the latter, this is not uncommon at all and much depends on the efficiency of your speakers and/or the noise level of your tubes. Get some new tubes tested for noise, i.e. they are graded as 'low noise'. This will solve most of these issues unless you have very efficient speakers that are revealing the noise threshold level of your electronics.

Is there a set of jumpers on the back that allow you to seperate the preamp section from the amp section? If so, seperate the two and put shorting plugs or Cardas caps on the inputs to the amp section. If you don't hear hiss, it's in the preamp stage, if you do, it's in the amp stage.

That's why it's really helpful for those seeking this kind of advice not to keep it a secret and actually give the name of the marque and model number.

Yes the hiss is the same in both channels and same volume (can hear it from listening position=unacceptable) with any of my 5 inputs selected at volume=0.

I tried an experiment this morning. I sent the tube pre section out to my el cheapo but zero noise t-amp and the hiss went down considerably. T-amp is 15 watts, integrated is 150 watts, speakers are a super efficient 104 db Klipsch LaScala.

Maybe the answer is find a low noise, low gain tube pre amp to pair with my T amp.

"T-amp is 15 watts, integrated is 150 watts, speakers are a super efficient 104 db Klipsch LaScala."

That's the problem. When you have speakers that efficient, you have to be careful matching your components, otherwise you'll get a gain related hiss like you now have. Can you list your entire system?