If the memory serves me well, I saw somewhere on the bmwtips.com a reference to a magnetic insulation of the power and signal wiring.
Check the post at
http://www.bmwtips.com/tipsntricks/XMRadio/xmradio.htm
and then check the
www.mcmaster.com for a part # 5756K31, this one is thinner than the film mentioned in the bmwtips post and about $0.50 cheaper per foot.
This process will not hurt the installation and it might actually help with the engine whine, and you can wrap all of your wiring without relocating it. This wrap would provide magnetic shield, while the ground loop isolator would provide electrical "shield".
You will need to use electrical tape to wrap the wires, I am not sure how good the adhesive is on the other part numbers that are sold on the same McMaster's catalogue page.
Also, as a good installation practice, once you finish the wrap using the electrical tape, you might want to use a small wire-tie to tie around the last loop of the tape, to prevent the tape from unwinding, when over time it will have lost its adhesive properties.
Keep us posted of your success (I have no doubt that with GLI and the tape you will succeed),
TerminatorX5
Have fun