Same problem here. Just got a new Droid 2 Global the other day. Paired it with my 2008 BMW, and every 45 seconds or so, there is an audible buzzz that last for about 5 seconds. During that time, you cannot hear the caller and the caller cannot hear you.
I've had many other phones (Blackberry Bold, Palm Pre, etc...) paired to this car with no problems at all. The hands free feature of my car is so important and useful to me, that if I cannot resolve this issue, this phone is being returned.
Whatever the issue is, it is clearly related to the Droid.
Hoping someone has a remedy.