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Loud rumbling noise coming from rear of 2006 Subaru Outback

I have a 2006 Subaru Outback. When I start it, it makes a constant rather loud rumbling noise that seems to be coming from the rear of the car. I can feel a little vibration through the steering wheel, but when I put the car in neutral the noise/vibration goes away. Any ideas? TIA.

How many miles on it? Have you kept all the tires about the same diameter?
My wild guess would be something inside the transfer case. They’re susceptible to damage from excess heat if there’s an off-size tire on the vehicle for any length of time. But it’s only a wild guess. It could be as simple as an exhaust leak.

If the exhaust recently has been worked on it could be as simple as an exhaust component installed too close to the frame and the vibrating from the engine is being conducted through the frame or other parts. You can do a little test by grabbing the tail pipe and shaking it. You should not hear any rattling or scraping noises.

But that is the easy fix.
I presume that you may have a problem with the rear differential. Check to see if there has been any leaking in that area. You could have a leak and now the Rear end lube is low. If so, have it filled ASAP before major damage is done.

It may also help to try going down a steep hill…and putting it in neutral. To see if the noise goes away then.


The OP needs to clarify exactly what “when I start it” means.

If those words mean…when you start the engine, but before you actually drive the car…then I have to discount mountainbike’s theory. On the other hand, if “when I start it” means when you actually get the car rolling, then it is entirely possible that this has something to do with damage to the viscous coupler (Subarus don’t have a transfer case!) as a result of mismatched tires.

Yes, this could be an exhaust-related problem, or it could be a viscous coupler-related problem, or it could be neither. As the old saying tells us, The Devil is in the details, and the OP needs to clarify the details for us.

Yeah, a bit confusing. If you mean when you’re moving it makes a noise from the rear, it could be a rear wheel bearing. We just had one replaced on our 2007 Forester, it was making quite a racket!

Yes, sorry for the lack of detail. The rumbling, which I’d also describe as sounding rough, starts as soon as I turn on the engine and when the car is in P, R or D. I actually have placed the car in N while moving and the sound does stop. It also stops when I’m at a red light and idling (with brakes engaged). Also, the rumbling does lessen the longer I’m driving, so I’d say it’s the worst when I first start the car to maybe 15 minutes of driving.

If it does it in Park, that eliminates the wheel bearings, differential, etc. My vote is something with the exhaust, such as a bad or missing hanger or heat shield.

If it’s rumbling in park I bet it’s exhaust.

It is almost surely the exhaust, which the OP can check when everything is stone-cold.
More than likely, one of the exhaust hangers toward the rear of the car has become detached and the exhaust pipe is “drumming” against some part of the chassis.

I agree exhaust, but I’d suspect a hole in the system, but it could just be a hanger.

Yup, your new post eliminates the entire drivetrain and make an exhaust leak an extremely high probability. Leaks like this can b e highly susceptible to the vibrations running down the pipes, and that can vary considerably depending on the what gear the car is in, whether it’s stopped or not, the engine load, and a whole host of other sources.

When you get under the car, take a good worklight and look for carbon tracks (black areas that wipe off with your finger) at the joints, especially at the “flex joints”.