That's strange, i opened mine a while ago and as far as i can remember there is no way the electronics could get into the arm/cartridge. The transformer is on the opposite side of the arm for instance. Is everything still original?
I believe most turntables use a small capacitor as a spark suppressor, wired across the switch. IIRC it should be 0.1 mf 250 v. If it is too big, enough AC can cross to make the motor vibrate when it is off.
Thanks for the responses. I will open it up and look into that capacitor or any faulty wiring. From what I believe as well, the tonearm wiring is completely indepentdent from that of the turntables; that's why I find it weird.