Same thing going on in my e90 sedan right now too. It's odd. I never heard it when I first got the car--only now after break-in. I have almost 3k miles.
OT, my mic in my Bluetooth went out today. They told me to erase the phone from the nav and take out the phones batteries for a few minutes. I did so, relinked it and now it works perfectly. Also, sometimes when I switch DCT off or to S5/6 my treble speakers go off intermittentl--which is strange as well. Don't know why that would be.
Back to original topic--basically, the turn noise is not bad as long as you can stand it? Is that the consensus?
☆AW ☆ e90 ☆ M3 ☆ DCT ☆ eighteens ☆no sunroof☆