My 2008 Subaru Outback has developed a very interesting sound. At start-up, idle and under 10 mph, the car sound completely normal. At about 15 mph a hard to describe low pitched hum/virbation (almost the sound you would hear is a small twin proped airplane at crusing speed or the sound a wood chipper makes when you turn off the engine but the blades and drive shaft are still spinning) starts and increases with speed. At 60 mph you almost need air plugs. There is no viration in the steering, the tires are evenly worn. There are no smells (like something hot or burning) and no dummy lights have come on. The sound envelops the entire car but seems to be centrally located or slightly rear of the car. Any ideas? Should I stop driving the car?
That sounds a lot like a bad wheel bearing. Does it change at all when you turn one way or the other? Jack up the rear wheels and spin them - listen for any kind of rough/grating kind of sound.
Either way I would likely only drive the car enough to diagnose it/get it to a shop and that’s about it.
I know this is going to sound stupid, but, change the position of the roof rack cross bars and see if that makes a difference.
I had the same idea and actually removed the cross bars but it had no impact.
Oh well just a thought.