My Oppo hums

With my new Burson PI-160, my Oppo now hums at the speaker with the volume turned up and when still connected via ICs and on another input, passes the hum on (albeit slightly with nothing playing). There is no OFF feature on the Oppo, just standby. It was never present with the older Burson or the Classic 6.1 that I still have. If I disconnect the Oppo, the hum is gone. The mickey mouse IEC has no ground plug and that may be the problem: won't know until tomorrow when I get one with a ground plug (if they make one) Has anyone else experienced this?