I am new to the boards and I just installed the avic f900 and received some great help from all of you about the ground mod. I was driving around today and trying the Blue tooth and trouble shot this thing with a friend on the line. I moved the mic to about 6 inches from my face and they said it was a thousand times better and crystal clear. I then mounted the mic on my visor so that when I am on the phone I can lower my visor to get the mic at the desired distance.
I have a feeling that the microphone is cancelling out the noise and if you are to fare away you will not be picked up. Give it a try and let me know what works.
Mike Anderson