Subtle pulsing sound on 2009 BMW 328i xDrive

My 328ix has the sound like a pulse going down the road around 40-60 mph. Not a thump thump sort of thing, but a louder hum ever couple seconds consistently? Where do I start? brand new Michelins with less than 200 miles. alignment, or x-drive issue possibly? thank you.

Asked by for the 2009 BMW 328i xDrive