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 may also want to try plugging the Mac into an extension cord and run it to an outlet thats not on the same circuit as your system. Also, if you know anyone who has the same computer, see if they'll let you try their PS in your system.
That's interesting - I use a MacBook Pro feeding an external DAC via USB, and I don't notice anything. I wonder if it's related to your power or if it's only an HDMI issue. Can you try USB and see if you have the same problem?

(btw - I had a pair of Meadowlark Kestrel Hot Rods in that system until last year. Great speakers. Looks like yours are even better now!)