I bought a Ortofon Cadenza Mono cartridge used a few months back and used it off and on by swapping in and out of my SME 3012R tonearm. Initially everything was quiet and sounding good. Swapped out the cart for another then put the Ortofon back in yesterday and I now have a hum. I tried countless grounding methods, cables even headshell. Still hums. Any clues as to what is causing it. Hard to ask for help from dealers since I didn't buy from them.