[StanD]

  Thanks for all of the advice. I would assume since there is no noise coming from the optical output, the iMac is good. I think it is something in the USB. I will continue until I figure this out!

Optical connections have no ground connections, thus are isolated.

 

[DDF]

Is the mac 3rd Gen actually cord? If so, it's a group discussion loop. The noise affects USB timing and interface noise. On mine, it was a swoosh in like waves as well. The USB isolator fixed it. Cutting ground wires on the USB didn't.

 

[DDF]

Silly android auto correct.... first sentence should be is the mac 3 prong ac cord?

 

[chuck8403]

It is a mid 2011 version. Yes it does have 3 prongs.

 

[chuck8403]

  Like I said a bunch of posts ago, it's most likely a ground loop. Here's a link to another USB isolator. These gadgets do not connect grounds between the ports of the isolator. The Schiit Wyrd does not do this. Also as another poster said, try using just the headphone out of your source to listen for noise.
http://www.amazon.com/HifimeDIY-Isolator-ADUM4160-signal-isolation/dp/B00F4SCCR2

Ordered one of these and the issue went away. Thanks for the tip!

 

[StanD]

  Ordered on of these and the issue went away. Thanks for the tip!

Great, I'm glad you don't have to put up with noise anymore and can enjoy music.

 

[chuck8403]

Never really notice it until I got the Bitfrost and HD700. Now the sound is so sweet!

 

[hmgp]

Same problem with the 2014 MacBook Air. Ended up getting a portable amp/dac, glad you fixed your issue!