An "AC buzz" is the 60 Hz noise one hears when a ground connection is bad or the AC cord is plugged in backwards. It sounds like your noise is much higher frequency.
Where is your equipment located? If you have your amp, preamp and source equipment located in the same rack as your TV or similar equipment, they may be the source. TV equipment in particular can emit a lot of EMI at higher frequencies. (Also remember the "off" switch on a lot of modern equipment doesn't actually shut off power to the piece of equipment. It just puts it in standby so the internal circuits are still live - and noisy.)
Try removing your amp from the equipment rack and powering up the speakers with the amp several feet from any other electronics. If that solves the problem, then add back the preamp and audio source(s). In lieu of moving equipment, you could also try physically unplugging the other items.
If the noise is still gone, that means your interference is coming from other equipment on the rack. You'll simply need to physically separate the audio equipment from your other stuff. Often just a couple of feet will do the trick.
Where is your equipment located? If you have your amp, preamp and source equipment located in the same rack as your TV or similar equipment, they may be the source. TV equipment in particular can emit a lot of EMI at higher frequencies. (Also remember the "off" switch on a lot of modern equipment doesn't actually shut off power to the piece of equipment. It just puts it in standby so the internal circuits are still live - and noisy.)
Try removing your amp from the equipment rack and powering up the speakers with the amp several feet from any other electronics. If that solves the problem, then add back the preamp and audio source(s). In lieu of moving equipment, you could also try physically unplugging the other items.
If the noise is still gone, that means your interference is coming from other equipment on the rack. You'll simply need to physically separate the audio equipment from your other stuff. Often just a couple of feet will do the trick.