Originally Posted by S0C0nFused
I would speculate that your issue is almost certainly your tires. What brand and mileage?
The tires are brand new Barum Bravarius. The previous owner changed them just before I bought the car. They seem like cheaper tires, but I can't see how the noise could be related to tires/bearings/etc. If I take the car out of gear at 70mph and let the RPM's drop to idle the noise goes away instantly. It is clearly related to the engine - some kind of harmonic drone. It's kind of a low frequency drone that actually hurts my ears a bit.
I ordered a new passenger side motor mount from Tousley Ford. I'll post if that makes any difference.