Actually the sound is more noticeable on the gain channel, so when i increase the channel volume to max and turn the master vol to 0 the noise is still there (yet reduced in volume) BUT when i turn the channel vol down to zero and turn the master vol all the way up i don't get any of the swishing sound. This tells me its the preamp tubes right?
Not necessarily, but more than likely. The best test to divide and conquer, would be to try another preamp, pedal or just straight plugged into the effects loop input, serial or set for 100% effects signal if parallel. This way you can just play the power amp and if nothing comes up, you can focus on what's before.