GEN4 Outback - speed related whirring/hum from center of car

[m1keb1ggs]

Hi guys,

After a road trip of a few hundred kilometers on the weekend, my normal "road noise" has definitely developed into something more. Since this is the first car I've had that's not a noisy V8 or Turbo I was told I was just hearing normal road noise when I first bought the car 2 years ago, but its a confirmed problem now...my wife is hearing it, and my 3 year old made a comment too

At low speed the car is literally dead quiet (love the EZ30), no crunching, clicking or grinding, but anything from about 40km/h up I can hear a growing hum or whirring noise that matches wheel speed. Best way to describe it at 100km/h is a small aircraft It's coming somewhere along the length of the center console between the front seats, and upon inspection the only real thing in the vicinity is the tailshaft carrier bearing. Giving this a wiggle shows probably have more movement in the rubber than I would have expected, which might explain the wobbling feel I get under low rev load when going up a steep road from a stand still or pulling away from the lights when I give it a bit; note it never does it at at any other time. The gearbox and diffs have good fluids and shift fine with no noises so I'm assuming (hoping) its external of them at this point

I'm hoping I'm diagnosing this right before I go removing the drive shaft for a rebuild $$$. Any chance it could be in CVs or Bearings? The noise doesn't change pitch or volume based on left or right horizontal loading, so cornering makes no difference, which I would have thought removes the bearing possibility. The only time the noise changes is with speed and dips or humps in the road when vertical load changes.

The front right inner CV has a zip tie on it, so I'm suss as to whether this even has grease in it. Giving it a pull up and down shows some movement in it, maybe a millimeter, and twisting it makes a few noises, but hard to tell if its just gearbox lash. For $100 to throw on another complete shaft it wouldn't be a bad start I guess. Even bearings at $120 each arent a bad replacement to make as part of the troubleshooting. But I prefer to not just throw money at it.

So in short:
-humming/whirring noise from center of car
-wobble under load, low revs and speed
-no change in noise around corners
-change in noise over dips or humps in road in road
-slight vibration, more a rough feeling in your feet at speed
-front right creaks when going over speed bumps, but I think that might be the aftermarket poly bushes...but could be related
-no squealing, crunching, clicking or high pitch noises at all
-not a pulsating wub wub wub or woo woo woo noise as some others have reported with tires, bearings etc.

I suspect:
-tailshaft carrier bearing
-tailshaft u-joints
-inner CVs
-...anything attached to the car that spins lol

Anyone had something similar?

[Adrian2627]

Before you go spending money on expensive driveline components get under the car and check the heat shields. There is one near the centre of the above the transmission which can cause such a sound. If that still doesn't fix it check the ones above the rear mufflers. The centre shield isn't really necessary and no heat related damage will be caused if removed.

[m1keb1ggs]

Interesting...how does it cause the noise? Do they rub on something? From memory they all looked fitted well and undamaged.

[Adrian2627]

Sorry Mike must have missed your reply.

Sometimes they will develop small cracks in the mounting holes which will lead to the vibrations. You may not always see them due to dirt, obstructions etc. Best to pull them off to check.

[Turbo Lag]

I had a very similar problem with the same kind of issues you're having.

viewtopic.php?f=15&t=19756

Turned out to be a wheel bearing. I've also now removed the heat shields as posted above.

[m1keb1ggs]

Long story short, I haven't fixed this yet...but...

I purchased hub/bearings, bottom balljoints and full axles for both front corners. I've replaced the hub/bearing, balljoint and axle on the front left, which alleviated the wobbling I was getting under low speed load, but the noise was still there. Because the axles were cheap $99 ebay items I got the terrible idle vibration in gear that every seems to complain about so I sent the axles back and am waiting for my semi decent Hardy-Spicer items to arrive, then I'll tackle the front right corner. Could still be the bearing or axle there. Both inner CVs/DOJs are stuffed, so I wont be surprised if its one of them. If not I'll start moving towards the rear. Very hard sound to place when driving. Just comes from everywhere, but the physical vibration/whirring feeling is in the front foot wells.

[BATMAN87]

Hi mate,
I had the same noise your describing as a small aircraft, between 80km - 110km/h, right after I done an wheel alignment on my previous lib. (which I neglected for 20000 km).
Bought 2 wheel bearings from Timken, which resolved the issue.

[m1keb1ggs]

Yesterday I finished the right side hub/bearings and bottom ball joint and put in a genuine reco tripod-inner axle ($169) on the front left which fixed the acceleration wobble, and I didn't get the terrible idle vibration I did previously with the cheap 6-ball eBay axles ($99). I was also supplied with a genuine reco 6-ball inner axle (not matching the other they supplied...idiots) which was going into the right side, so there's still that one to swap out...but all this could still be rear bearings, so hard to tell where its coming from. While driving today I actually noticed some noise difference when cornering left and right suggesting bearings, so I'm preparing myself for that to be on the list next

Car feels so much better after just one reco axle and some bearings.

Below is a pic of my knackered factory axle (green) along side the reco tripod-inner. Note the scalloped outer casing and criss-crosses on shaft. The smoother outer case on the right side is the reco 6-ball inner and would have no doubt vibrated like crazy at idle, so I didnt bother putting it in...take my word for it, I sent it straight back for a proper one. Axle guys and auto shops will swear blue in the face there's no difference, but set them straight from the get go. Don't waste your time, get the tripod inners only! Actually, just get genuines as a rule of thumb and save yourself the hassle I've had this last month

[zch91]

+1 to the above

I also purchased a cheap driveshaft off eBay (same as far right) and it was absolutely horrible to drive

I reconditioned my OEM shaft and the problem was gone and back to smooth driving