Like I said I am following this thread since I have the exact same problem. After my mechanic looked at everything 2 weeks ago and found nothing and the noise was gone it has now come back. On the way home last night from Orlando it went from a mild thump to a vibration and loud growl at speed to the thunk thunk thunk at 3-5 mph. Also noticed a lot of grease/oil around the boot and on the bottom of the car right above the inner boot. I can't find any tears or holes in the boot but it's to heavy to have come from the engine. Since this is a fairly new (less than a year) axel shaft it is under warranty so I will try and have it replaced tomorrow.