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Subaru Outback suddenly gets loud on the highway

I have a 2011 Subaru Outback with 40000 miles. For the third time since I’ve had it (6 months), the engine suddenly gets very loud at highway speeds while I am on cruise control. The RPMs go up about 500 and this lasts for a few minutes before going away. What is going on?

How loud is loud? Like an exhaust noise or a metallic noise or a roar or what? Little help, please.

If the engine noise rising 500 rpm is the “loud” noise you likely have a transmission problem. I assume you have an automatic not a manual. The torque convertor clutch might be disengaging causing the engine to speed up 500 rpm.

The noise and the rpm go away at the same time, right?
Are you climbing a hill when this happens?
Does it do away when you get to the top of the hill?

If that is the case, the cruise control may be just keeping the speed up and everything is operating as it was designed. Try driving the same route without the cruise on a watch your speed carefully. Hold the very same speed yourslef and see if the very same thing occurs.

The noise is more like a roar. Twice it happened on a flat section of highway, once going up a hill, but I know what it should sound like if it was just the RPMs increasing to drive up a hill with the cruise engaged.
It is an automatic. Why would it only last a few minutes and then go away?

I am going to assume that this 2011 Outback has a CVT, as very few came with a manual transmission, and you had to opt for the 3.6 liter six-cylinder engine in order to get a “conventional” automatic transmission. So…am I correct that this vehicle is equipped with a CVT?

I believe that Mustangman was on the right track, and that the problem is likely to be transmission-related. It is normal for a transmission to downshift on an upgrade, but if the trans is downshifting on a flat surface, there is almost surely something wrong with it. The downshifting, while not normal on a flat surface, would account for the increased noise as the RPMs increase.

In view of the relatively low odometer mileage, this vehicle’s Powertrain Warranty should still be in effect. So, I strongly suggest that you go to a Subaru dealership and have them check the transmission while the warranty is still in effect. However, don’t tell them to check the transmission. Report exactly what is happening, say that you suspect that the trans may be malfunctioning, and allow them to run the tests that they feel are appropriate. If you tell them exactly what to do and it turns out to be a blind alley, you will have to pay for that blind alley.

On any type of automatic transmission–be it a conventional one or a CVT–the fluid should be changed every 30k miles, so that is something to bear in mind for the future. With any automatic, using the correct type of fluid is very important, and with a CVT it is even more critical. When you have the trans fluid changed, I would suggest that you go to ONLY the dealership or to a professional, independent trans shop.

Whatever you do, do NOT go to a chain-run place like Lee Myles, Cottman, Mr. Transmission, or (God forbid!) AAMCO.

Yes it is a CVT.

Or, you could go to dealer and they might say, oh that blue outback with the funky trans. The last owner had it in several times trying to fix odd trans issue than they finally traded it in. Dealer may have service history for newish car.

Thanks. I’ll make an appointment with the dealer.

Agree with VDC. It should have been serviced at 30K anyway so this is a good opportunity for fluid changes.

Agree. I have had two Subarus and the motor did growl at certain RPMs with the four. But if the noise is recent and not continual, it will need someone experienced in both the motor and the cvt to evaluate it.

Before assuming it is the transmission, probably worth the time to put it on a lift and search for any exhaust leaks, missing exhaust hangers, etc.