Speaker Hum Question

I'm fairly new to the high-end audio scene, and just took delivery of my new system last night. I set up the system myself, and it sounds fantastic, and I expect it will get better as everything settles in. Here's my question: there is a very slight hum/buzz (very VERY slight) from the right speaker's tweeter that is present when the source component isn't playinhg, even when the preamp is in standby mode. The noise is not audible or distracting when music is playing. there is no corresponding noise from the left speaker. I do know that the electric line is not a s clean as it could be -- it is not grounded properly. This will be remedied soon, as I am having a dedicated line installed. Could this be the culprit? Is the noise anything to be concerned about, or is it just me being overly paranoid?

System:

Sonic Frontiers Line 1 Preamplifier
Thorens TTA 2300 Amplifier (dual mono, 120 WPC)
Joseph Audio RM25Si Loudspeakers
Sony SCD-1 SACD Player
Jolida Tube Tuner
Audio Quest Viper interconnects
Transparent Plus Biwire Speaker Cables
Monster Power 2000 Power Conditioner