Recap: I was hearing a thump thump thump noise at low speeds and while making turns to the left and right. At higher speeds the thumping frequency increased until it was a definite whirring noise which made talking and listening to the radio difficult. This forum made some suggestions and I set up an appointment with my BMW dealer.
Ok I had the car seviced and thank goodness I wasn't crazy. The car was making an awful noise from the rear end and yes the dealership heard it too! The problem was, in fact, a bad wheel bearing. They also noticed a click in the steering column when turning the wheel which was listed in a service bulletin I believe. All in all a successful solution to the problem. Now the car runs as quiet as the day I purchased it and the joy has returned to my life. Thanks for the suggestions and hopefully I will enjoy thousands of miles of driving pleasure.