Hum/Buz fro JC1

is your cable tv near the system? if yes, it may be that you have a ground loop. try disconnecting the coax cable from the cable box and then turn on your system to see if the hum is gone.

Houstonreef, have you tried what I recommended?

Do nothing with the cable jack. You may still want to try disconnecting the coax cable at its first entry. If you have a ground loop that causes this humming, you will know it when you take out that cable. Your amp may not be sensitive to this ground loop, but your preamp may be, since you say the noise is gone when you disconnect the preamp from amp. Try it, if it's not a big deal. Other than that, it could be your preamp that's causing this problem. Tubes, other things......who knows. Also try a cheater plug as recommended above.

it could also be that your rca jacks from preamp to amp are not seated all the way in the amplifier input jacks. If you are using locking type rca connectors, then you may want to make sure they're pushed all the way in. Some input jacks make it seem like they're in all the way, but in reality there's still room.
Also, try connecting your cd player to the amp(but don't hit play) and see if that causes the same buzz as the preamp does. If not, your preamp is causing your problems.