gymrat...that's almost undoubtedly wheel bearings.
Test it on a highish speed turn. The loaded wheel will 'whoop whoop' ...so left wheel on a right hand sweeping turn. If you're hearing it on a straight, it might be tires or a really bad bearing. See if you can change the sound from different direction turns.
With a tire, it could be a bad flat spot from having sat for a long while at normal or low pressure. After a couple of weeks of sitting, you can usually work it out...but if it's sitting for a long while, that flat spot might be permanently in the tire.
Still, the sound 'sounds' like bearings to me. Test it on turns and see what you get.
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Mangofy your E46!