It’s possible that nothing is wrong, and that the bleedthrough is inherent in the design. But in any event the fact that there is no bleedthrough from the aux input to the CD input suggests that the issue could be resolved by putting shorting plugs on the unused inputs.
Googling "RCA shorting plugs" will probably lead you to some suitable low cost choices (as well as some unnecessarily expensive ones). Or you could make your own, by obtaining some ordinary RCA plugs and soldering or otherwise connecting the plug's internal connection points for the ground shell and the center conductor together.
Regards,
-- Al
Googling "RCA shorting plugs" will probably lead you to some suitable low cost choices (as well as some unnecessarily expensive ones). Or you could make your own, by obtaining some ordinary RCA plugs and soldering or otherwise connecting the plug's internal connection points for the ground shell and the center conductor together.
Regards,
-- Al