[LAU] delta 1010 background hiss

Hello all... after getting a test machine (32 bit / fedora core rt kernel from planet ccrma) up and running with my delta 2496 configured correctly (with your help) and recording. I decided to take the plunge and setup my larger server which was dedicated to ms windows audio. This is a 64-bit machine with 2x-quad cores and 8GB of main memory. In it is also my main interface, the delta 1010. I setup a dual-boot with the exact same configuration that I did on my test machine. Everything is functioning as on the test machine with one notable difference: The delta 1010 has ~-30db of constant background noise. This background noise doesn't exist in the windows boot. I thought it might be my older mixer (from which 8 direct outs go into the delta 1010, but after turning the mixer off and unplugging everything (i.e., no inputs to the delta 1010), there is _still_ this hiss. I would like to attribute it to system noise but then why don't I hear this when I boot into windows? I'm basically at a loss here. I have jack running, routes to and fro software/hardware appear to be entirely correct (I can record and play and monitor). Just to conclude, I have the minimal going: qjackctl up and running, jackd started and the envy24control mixer up and the mixer shows this hiss. Any help here would be very welcome. Thanks in advance. David