I'm having a noise issue that just popped up.  I'll try to explain exactly what's taking place but it's totally unacceptable and could use some help.

My "normal" input chain is this: 

Mic > A-Designs Pacifica > A-Designs Hammer EQ > Chameleon Labs 7802 Opto Com > Mytek 96 A/D > Multiface II via SPDIF > DAW which is Sonar 8.53.

This works beautifully.  No issues at all with noise.

"Mastering" input chain is this:
After I do a mix, I've been (lately) going out of the Multiface II and BACK through the Pacifica > Hammer > etc.  THIS IS WHERE I'M EXPERIENCING WAY TOO MUCH 'COMPUTER NOISE'. 

(So the difference between the "normal" input and the "Mastering" input chain is a loop back through the Multiface via analog outputs 3/4 going into the line inputs on the Pacifica (instead of the XLR mic preamps on the back of the unit)).

I've eliminated the analog cables (using Monster Cable S 500 cables) by trying other cables.  I've eliminated the digital cable by trying different coaxial cables AND optical cables- all make no difference.  I've eliminated the Mytek because when in the "Normal input" all is well.  I'm thinking it's something with the looping via the MultiFace because when I unplug the two analog cables at the MultiFace- the noise goes away. 

Could this be a clock/syncing issue?  (I'm not using a word clock).  The noise is very evident and unacceptable and I'd love to try to resolve it.  Further, I'm not bashing the MultiFace at all.  It's been a workhorse in my studio for three years now.  Just trying to resolve the issue.