Meier, what set of tires do you have on your coupe? Low quality tires are the biggest causation of road noise.

Edit: Yeah...

 

I agree with tires being main cause. Also, check to make sure your wheel bearings aren't failing as those contribute to road noise as well.

My '06 sedan is quiet on the highway. Only time it got loud was when my wheel bearings were failing, and my exhaust miffler flange rotted out.

 

If you have so much noise that you have to turn your volume to 25 kinda tells me it is not the tires, especially if it sounds like it is from the rear of the vehicle. I would definitely say lean more towards wheel bearing issues which is common with G's.