This is a common problem on many phono stages. The signal is most likely coming through the air as Almarg stated. One simple and effective solution is to attach a ferrite core to the ground wire between the turntable and the phono preamp stage. You can get these at Radio Shack (or through Audioquest, ect). If you can find it TDK made a RF noise blocker ferrite core that works well. If you find one experiment with the number of turns that you wrap the ground wire through the ferrite core. Note: RF and EMI noise is mostly unnoticed by Audiophiles until the noise is removed from the circuit, then they realize that it is one of reasons that they were unhappy this the sound of their phono setups.Etbaby, I've been looking into what you are saying and I'm not sure what I need. Do I need to get one of these clip on ferrite cores for the power cord as well as the ground wire/rca plugs? Should I wrap the ground wire around one of these things as close as I can get it while still reaching the preamp?
Thanks for the help.