There are times not often but times when I go to lower the tonearm when I touch the lever I get a hum.
Rega grounds the tone arm tube to the phono preamp using the shield of the left channel of the phono interconnect cable. It might be the connection of the outer shell contact of the IC to the RCA jack on the phono preamp maybe corroded and not making a good low resistance connection. You might try unplugging both the L and R channel ICs from the phono preamp jacks and plugging them back in repeating the process several times. That should clean the connections.
If that doesn't help you could install a small gauge stranded insulated ground wire from the TT tone arm to plinth support nut on the under side of the TT and connect the other end of the ground wire to the ground lug on the phono preamp.
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