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2015 subaru outback motor hum

The car has a hum which starts at 50 ends at 55. Hum didn’t rise when i accelerated but stayed the same pitch until i hit 55 then stopped. Tried 2 different roads. Thanks for any help.

Are you the original owner?
How many miles does it have?
Have you rotated the tires IAW the owner’s manual recommendations?
Have you replace any single tire?
How many miles do the tires have on them?
Is there any abnormal tire wear?
Can you post photos of the treads?
Has the car been aligned recently?

Subies need their wheels to all be close to one another in diameter or they’ll develop problems with the powertrain. Your owner’s manual defines this.

In addition, tires when they get to the point of approaching the wear bars can become noisy, especially if there’s an abnormal wear condition.

It’s important to get the most common causes resolved before beginning to address possible mechanical issues. Post photos of the tires’ treads and we’ll start from those and the answers to the questions.

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Do what mountain bike says. Then get back to us. It’s important to eliminate the easy things first.

It could be a piece of molding or a seal or something else that has loosened a bit. My brother has an Accord whose windshield seal made a vibrating/humming noise at about 60 and then went away at about 70. The belt is also a possibility but unlikely.

All tires worn the same.
Rotated twice
35k miles
Flat drivers side rear fixed, did not replace.

There’s not much tread left. are the wear bars even with the tread? You could try replacing the tires and see if that works. I wouldn’t ordinarily suggest throwing parts at a problem, but if you need tires anyway, it’s worth a try now.

Subaru’s maintenance schedule calls for tire rotation every 7,500 miles, but yours have been rotated only twice in 35k miles?

Even though the tread wear appears even to the naked eye, it is possible that as a result of not doing tire rotations as specified, there is now excessive wear in the Center Viscous Coupler.
Would that produce the type of noise that you described?
Maybe yes, maybe no, but I would suggest that you buy new tires in the very near future, and then resolve to rotate them every 7,500 miles.
With any luck, new tires–coupled with on-schedule rotation–will give you a quieter driving experience.

getting tires this week. Had a problem with one rear tire. Slow leak

When we get them changed should I have the dealer check the drivetrain even
if the noise goes away?

Good photo.
I pulled out a new quarter and a ruler. You have between 2/32" and 3/32" left. Your tires are too worn to protect you on wet or otherwise bad roads. And at that amount of wear, they may well be the source of the noise. Worn tires can be noisy.

My recommendation? You need to anyway, so get the tires replaced with a good quality tire. Post back with the results.

If the noise goes away, I’d leave it alone. If you ask the dealer to find something, they might recommend work whether you need it or not.

There are probably a number of tire dealers near you. Why go to the Subaru dealer for tires? It’s your choice; I just thought I’d ask.

I won’t go to them for tires. Dealing with the several recalls since we
bought the car hadn’t filled us with confidence.
Really appreciate your time and expertise.

Your title implies the hum is from the motor. Why do you think that? B/c from what you say later it doesn’t sound like a motor-related problem. Try some experiments to see if you can narrow down more what’s the source of the hum. Go at 50 mph where you hear the hum, then shift to neutral. How does that affect the sound? Now increase to 60 mph, shift to neutral and coast down from there to 40. What do you hear then? Then go back to 50 mph, stay in D, and lightly tap on the brakes. Does that affect the hum? Try other gears, etc etc …

As you are buying new tires anyway … and b/c the hum could be caused by the tires … here’s my recent tire buying experience.

I had to buy 8 new tires last summer. I’ve always used Costco for tires, but they no longer offer the size of tire used on my Corolla. First I reviewed what Consumer Reports said about the various brands of tires that fit my vehicles, and decided what brand and model I wanted. Then to find a place to buy the tires I searched for tire stores using a combo of Googling and Yelping and from that decided which the best-customer-rated tire stores in my local area were, then paid a visit to each of them, pricing them out, and seeing how cooperative they were. What I found was there wasn’t that big a difference in price store to store, but there was quite a big difference in the level of professional-quality service and cooperation they provided. It’s all a bit of a chore, but I ended up getting good results that way. Before making your purchase check the tire company’s websites btw, as they may offer rebate coupons there. I found one for a $70 rebate that way.

Thanks for the reply, we’ll see how the new set of tires affects the hum.

I found that Costco did not stock tires in the correct size for my Miata, but they told me to order them on-line at the Costco website and they would contact me when they arrived. I did that, it took about a week, and I called the store and made an appointment to get them mounted. It worked out very well. It is possible that, for a person working days, appointments might be tough to get at Costco.

For some reason they don’t offer the Corolla’s size even on their website. I think the brand of tires they offer, e.g. Michelin, have all discontinued that particular size. Hankook still sells that size, but that’s not a Costco brand apparently.

As Subaru’s AWD appears to be especially sensitive to mismatched tire circumferences (actually revolutions/mile), to ensure you get a matched set when replacing yours consider measuring the circumferences before mounting and again after inflation, aiming for a spread not exceeding 0.25 in. (other AWD mfgrs specify 0.5in). Aim for tires with matched date and tooling (mold) codes. While recently purchasing a set for our Outback I found one tire (same date code but different tooling number) to be ~ 0.35in. larger circumference than the other three despite nearly identical tread depth. If this isn’t practical, consider Tire Rack who will measure and match for you.