Are the phono cables routed near any power cords, power supplies, or components that may be inducing hum in them? Did anything change in the system or its physical setup around the time the problem appeared?
Also, my suspicion would be that if connecting the ground wire makes the system sound "less lively," that having it not connected is somehow compensating for some other issue. If you haven't already tried this, see how the system sounds with the wire connected and with the resistive loading changed to a much higher value than the 100 ohms you have been using. The relatively heavy 100 ohm load may be adversely affecting dynamics. (I note, btw, that 100 ohms is the **minimum** load impedance recommended for the AT-ART9).
Regards,
-- Al
Also, my suspicion would be that if connecting the ground wire makes the system sound "less lively," that having it not connected is somehow compensating for some other issue. If you haven't already tried this, see how the system sounds with the wire connected and with the resistive loading changed to a much higher value than the 100 ohms you have been using. The relatively heavy 100 ohm load may be adversely affecting dynamics. (I note, btw, that 100 ohms is the **minimum** load impedance recommended for the AT-ART9).
Regards,
-- Al