Buzz through speakers w/amp on & pre off

I'm experiencing a buzz through my speakers which makes it impossible for me to leave the amp on continuously. It only happens when just the amp is on. If I unplug the preamp the buzz gets slightly quieter, and if I unplug the cd player the buzz gets quieter, but barely enough to notice.

The second I turn on the preamp the buzz goes away completely. The second I turn off the preamp the buzz comes back. It doesn't interfear with listening, but I would like to be able to leave the amp on all the time.

Has anyone ever experienced this?

Here's what I'm using.
unmentionable cdp
Anthem Pre 1L
Classe ca-200
Thiel 3.5
It buzzez both with and without the Thiel EQ box connnected.

Any thoughts?
Could be a ground loop. Try a cheater plug on your amp, then move it to your pre. Just went through same thing. Cheater plug on my pre solved it.

Cheers, Spencer
I thought that it was unwise to have the amp on with the pre-amp off.
You should never keep your amp on if your pre is off...either keep both on or both off.
Leave amp and preamp on all the time, or turn both off at night. Amp on without the preamp can do this, and I've heard it is unwise...I'm no engineer, so I don't know why, but I leave my amp and preamp on all the time.
A ground loop is a voltage potential difference between components usually caused by running equipment off several different outlets..i.e one outlet for amp, and the other for components. The fix is to lift the ground, or put all on the one AC source for same voltage potential. Short of That..or improper or bad wiring in could be internal to the amp.