I have a Marantz 7300OSE that I am trying to connect my turntable to. The receiver does not have a phono input so I bought a phono preamp. The problem I am having is with the grounding. I connected a ground wire between the turntable and the receiver but Iam still getting a hum. In connecting to the receiver I have tried a screw on the back panel and the am ground with no luck. Any suggestions? Thanks!