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Loud rumble while driving at highway speed

Hi folks! I’ve got a noise that’s driving me crazy that I can’t diagnose. 2006 Subaru Outback, 2.5 naturally aspirated, manual transmission with 220,000 miles.

At about 45 mph and higher, a loud sound that sounds like road noise begins. A constant rumble, not a howl or ticking sound.

  • It gets louder with the car’s speed (not engine rpms).
  • The frequency increases slightly with speed, but it doesn’t seem like a 1:1 scaling of speed to frequency.
  • Sounds like it’s coming from below the driver’s seat, but it’s hard to locate.
  • The noise goes away if I turn the steering wheel to the right, like on a highway exit.
  • Noise continues if I shift into neutral.

What I’ve done:

  • Replaced all 4 tires (they needed to be replaced anyway)
  • Replaced front driver’s side wheel bearing

Anyone have any ideas? The only thing I can think is that I replaced the wrong wheel bearing… But it definitely sounded like it was coming from the driver’s side! Anyone have a yea or a nay before I spent another Sunday afternoon messing around with a slide hammer? The bearing assembly I removed appeared to be in good shape, and I think I the play I found on that wheel just means I also need new tie-rod ends. Is there anything else that would cause this sort of noise?

Quite possible that L/F bearing could have been in need of replacement and it’s possible there is/are another/others.

AWD? I believe Subaru AWD systems have bearings supporting the driveshaft to the rear wheels. That’s another possibility… the support and/or bearing.

Yup, passenger side wheel bearing. They can be tricky little buggers to identify. I once replaced a drivers side bearing when the passengers side was actually bad. With 200K on the clock, it isn’t a wasted exercise in any event. And as CSA says, there are bearings UNDER your car that could be going away.

Thanks, guys! I hadn’t even thought to look around the driveshaft. This is my first AWD car and I haven’t quite wrapped my head around the drivetrain. So my current plan is to replace the front passenger’s wheel bearing and check for play or broken boots around the transmission/driveshaft. And yeah, I figure anything I replace on this car needed to be replaced anyway, so no big loss on the driver’s side bearing (except a Sunday).