Welcome to the VE,
Since you get the hum when you touch the tone arm or cartridge it is probably due to a poor ground conection between the tonearm and the turntable chassis.
I don't know your TT but there is a manual in the library which contains a lot of info, although this may not help.
If you have a test meter it would be worthwhile checking continuity between the tonearm and the groundwire from the TT; if this is poor then you can trace it back towards the arm and you should be able to identify where there is a poor connection.
Thorens TD521, SME3012, DV-20X, Creek OBH 18, Cambridge Audio A5, Cambridge Audio P500, Castle Chester, Creek OBH 21SE, AKG K702