Is the RFI problem channel (its cable, for example) closer to a window? Is one side's cable looped (acts as an antenna)? Try turning the phono or pre 90 degrees... Stuff like that can impact in-city RFI problems. Where I used to live, there was so much RFI coming in the windows, I had to move the system (minus the speakers) downstairs. Nothing else worked (RFI blockers, cable wraps, etc.)