Earth hum

I use a Reflex M with my turntable (Pink Triangle LPT VX with Funk Firm FXR tonearm). Very occasionally I get earth hum when I switch on my integrated amp (Arcam FMJ A19). This can happen if I move the Reflex M slightly. Usually a jiggle of the earth wire (connected to the rear of the Reflex M) will solve the problem, sometimes I need to unscrew it and then reattach it. Sometimes a jiggle of the wire seems to cure the fault. I think, it's hard to tell sometimes which action has done the trick. Incidentally, if I disconnect the earth wire the hum goes away. So I'm thinking the possible problem areas could be: the Reflex M, the earth posts, the earth wire itself, the turntable end of things, the tonearm wiring. Any thoughts on how I go about eliminating the possibilities?

Thank you, Graham.