Cause of speaker static?

Rare is the system that is stone silent when running. Probably just system noise from the amplifiers and preamp. Tubes are ususally a bit noisier than SS. Unless you can hear it from 12 feet away with nothing playing, don't worry about it. Otherwise, something is probably wrong with a component or interconnect.

Stooges. If you are attaching any VCR to the preamp, this could be the problem - related to the cable input to the VCR . Try removing this VCR input and see whether the noise goes away. I had the same problem, and found the TV/VCR connection to my system to be my problem. Cheers,
John.

Let's see, the noise goes away when you turn off the preamp... Then unless you are using a tube CD player or tube DAC, your preamp is very likely inherently noisy, and the source of the noise.

If you are using a tube source component ahead of the preamp, then it could be that the source is the cause. Turn off the source component while leaving your preamp and amp turned on. If the noise goes away, it's the source component, otherwise, it's your preamp. The higher the input sensitivity of your amp and the higher the efficiency of your speakers, the more apparent the system noise floor will be.

Some tube preamps are just plain noisy. Changing to low-noise, low-microphonic tubes may help some, but could be wasted on other designs where the circuit design is fundamentally noisy.

Incidentally, if you had bothered to mention which preamp you are using and which specific source components, it would have been much easier for us to pinpoint the problem and make more specific recommendations.

DAC's occasionally emit scary sounding, crackly static. Turn off the power amps, toggle the input switch on the DAC, turn the DAC off and on, restart the power amps.

If you've got a tube preamp...listen as you whap the preamp with the palm of your hand. This sometimes works with tubed guitar amps but it's not usually a permanent fix :-)

I completely agree with Rockvirgo. Digital components can be realy noisy. The biggest source is power line.
1. Try to use a good quality power cord
2. Try to connect your digital source onto the different power line or to the power conditioner/power plant.
The same tweaks I would suggest to do with your preamplifier.