More investigation reveals that there are two problems with the 2011 Bluetooth mic. First, cellular interference depending on phone position, depending on where the phone is, loud buzzing. Second, if you find a no buzzing position, driving the car will cause road noise in the car to drown out your voice.
Next problem, non-replaceable microphone. If you take the mic down and pop off the small clip on the cover, you will find a small circuit board which is connected to the mic. This might be some kind of attempt to implement hardware noise deduction, or digital signal conversion. Either way we lose.
To fix bluetooth audio, stereo head replacement, with standard noise cancelling Bluetooth mic.