Noise in line from MacBook Pro charger

I am using my MacBook Pro with an external HD to feed the Oppo 105 via HDMI

When I plugged the AC charger in I am getting a very pronounced more or less rhythmic sound

Unplug and it's gone

Any ideas?
You have a good ac pollution is real-just use the battery for music if you can. Otherwise Shunyata and other manufactures make products to stop/restrict this noise