Noise Rega standard RB250

Already did that, and no issues. When the 4 wires just han in the air the right channel is silent and the left channel have noise. It's the same with cartridge connected and RIAA connected.

Did you swap the left and right turntable RCA plugs at the preamp inputs,
and verify that the noise changes channels?

Do the plugs fit tightly on the sockets?