Rear end noise on '12 base Impreza sedan

40

Asked by ImprezaNoob Aug 23, 2017 at 10:36 AM about the 2012 Subaru Impreza 2.0i

Question type: Maintenance & Repair

I took my car in for it's 75k mi maintenance, where they replace all the fluids,
spark plugs, etc. After getting my car back, I noticed a hum that seems to be
coming from the rear of the car. It starts at about 25/30mph at a low
frequency, and gets moderately louder as I speed up, with a correspondingly
higher frequency. It reminds me of the tire noise that those lifted and modded
pickup trucks have.
https://youtu.be/sH1Y2hh0GGg
I initially thought bad tires, but I would have noticed tire noise as loud as the
normal air/road noise prior to the service, and it doesn't change on different
surfaces. I got my tires balanced, but it didn't change anything.
Then I thought wheel bearing. It sounds about right, but the noise doesn't
change while putting more weight on one side or the other, or during
accel/decel, aside from pitch.
And I don't have a place or jacks to jack my car up to do a lot of the
diagnostics myself. Does anyone have any thoughts?

16 Answers

13,220

I was thinking wheel bearing like you said. Dust shield rubbing rotor? Caliper sticking? Brake pads getting low..squeeler touching? Some thoughts

Best Answer Mark helpful
40

They did say my rear brake pads were getting low, but I'd be surprised if it were the brakes. There isn't any audible grinding at low speed, braking is consistent and without squeal, the noise doesn't change under braking, and a simple tire rotation shouldn't have touched the brakes (unless I got a really ham-handed tech). Thanks for the thoughts though, I may get the brakes done and see if that fixes it.

13,220

I do not trust mechanics. I know I will get some comments on this but early in my life I got taken advantage of and "stolen" from. This is why I took on car knowledge. I can see them creating a noise so it scares you to get you to bring it back. I have seen many friends and family "almost" get shafted from automotive repair. They now have me to either do it free or advise them on situations. I hear so many people say they took their car in for one thing and when they got it back something non-related had a serious issue. Not a fan of this service industry.

2 people found this helpful.
40

I don't trust them much either, but apartment living doesn't lend itself to working on your own car, sadly. I doubt my local dealership would go as far as damaging my car, but they sure as heck price gouge. (I mean, like $100 for replacing the cabin and engine air filters? I'll spend 10 minutes and save myself $70 of "labor")

2 people found this helpful.
12,325

If it doesn't change by turning and putting weight on either side of the vehicle, I would maybe suspect the rear diff or the drive shaft (but I think they squeak when they wear out). I wouldn't go to a dealer. I'd find a quality mechanic in town (verify reviews via facebook and google) and start with them. Someone else just had their subi worked on at a dealer and a week later had their headgaskets blow. I'm skeptical of their situation. Very unfortunate. You could try recording via video/sound with your phone.. put it on the very right, middle, very left, etc in the rear and see if you can pinpoint a location that is much louder. Maybe even cover it with a bowl to concentrate the noise from that area.

1 people found this helpful.
27,350

Rear wheel bearings on Subies will NOT change acoustically when varying side loads. I', 90%+ sure you simply need a RWB. Be careful because the 2012+ Imp's bearing is slightly different in mounting depth than others, so match it up perfectly. You might have to get the pricey ($180) one from Subaru. Otherwise it's a simple one hour job. be sure you replace the correct side, too (use a stethoscope to check up on a lift).

1 people found this helpful.
40

Yeah, I'm skeptical of my dealership. I mean, I took it in, and suddenly, I have noise, and need new bearings at 75k miles. I'll have the local shop take a look into it while they're doing the brakes. (Unfortunately, I don't have the equipment or place to do the job myself) I'll let you know how it turns out. Thanks.

2 people found this helpful.
12,325

omg...firstly, you might request it be towed to avoid anymore wear on the spindles/knuckles. Secondly, you might ask the new mechanic to document findings, maybe even with pictures. Then after his conclusion, ask in a roundabout way whether or not his findings would have worked themselves loose in a short matter of time. Bearings last a looong time, generally. And they shouldn't just all of a sudden go bad. There are good dealers and there are bad ones. I'm not trying to talk bad about dealers but this is exactly why I avoid them. Plus their prices are usually astronomical.

40

I used ye olde emergency jack to check if there's any bearing wobble on the back right tire. Lo' and behold, there's rubbing and no wobble. The bearing's fine. There's a slight abrasive sound on each turn of the wheel corresponding to increased resistance to spin the wheel. Something's touching the rotor. Now, should I have the dealership fix whatever they bent out of shape [for free], or just get the local shop to fix it while they're doing my brakes anyway?

12,325

Is it combo disk drum brakes with the enclosed shoes? Sometimes get a rust spot that'll rub with new rotors, yeah?

1 people found this helpful.
13,220

If it is the dust shield (thin meta disc on inside of rotor 85% around rotor), I would have new shop bend it back. I would call dealership and let them know their error. This is me...I let them know I am not happy!!! As you read my other posts about stealerships and most mechanics.

2 people found this helpful.
27,350

Crooked backing plates are extremely common, and difficult to catch without a test drive followup. This is a truly minor annoyance of no consequence. Just be grateful it's nothing else.

27,350

Noob, the brake rotor installer will automatically check for clearance with the backing plate. Asking two different wrenches to get involved is silly.

40

Yeah, the dealer probably accidentally knocked something while doing the rotate, but I'm sure the brakes place would notice the rubbing if the brake job didn't fix it in the first place. Thanks all, I appreciate all the advice.

27,350

Your static test for bearing wear is insufficient. You REALLY have to get your beast up in the air and check acoustically with a conductive tool (long screwdriver to ear) or stethoscope. Again, Subie wheel bearings are a VEREY common failure...but so are simple crooked (or gravel-filled) backing plates.

Had the same thing happened to me on my old protege5. Switched to summer wheels &tires, humming started as I rode off. And indeed it was 2! Bearings. Winter tires softness dampened the humming. Stiifiers summer ones amplified it!.

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