Newly acquired 1010 has a hum when using phono. I've tried 2 tt's, pioneer pl117d and technics 1200 mk2, both hum in phono 1 and phono 2, but don't when hooked up to the onkyo. Is this a ground problem? If so where can I look to test phono ground. Also no hum with am, fm, aux. Thanks in advance for any suggestions.