Low Rumble Like Noise at 50-65ish MPH

All,

 

I recently replaced both rear hubs, and the wagon is super quiet. What I can hear now is a low frequency hum or rumble like noise which "seems" to be coming from the back of the wagon. It starts to become audible right around 50mph up through 65-70ish. It seems to go away between 70-85ish and then comes back at around 85+ mph. The noise is not gear dependent. It is constant with the speed of the car, even when I put the tranny into neutral or push in the clutch. Could this be the rear diff singing its goodbye?

 

Thanks for the ideas and help,

 

j.

Have someone ride in the back seat while you drive, you can hear all kinds of things from back there.

 

When was the rear diff changed ? what fluid ?

Have someone ride in the back seat while you drive, you can hear all kinds of things from back there.

 

When was the rear diff changed ? what fluid ?

 

My 8 year old daughter was the one who noticed the noise first

 

The rear diff is the original I believe; 225,000 miles. Last fluid change was at 212,000 with Redline.

 

j.

FWIW, I only use Moto Gear 300 in these cars for the 5mt and the rear diff.

 

I have not had good results using other fluids.

 

I use Amsoil 5w-40 European Classic and their EA15K13 filters in both my cars doing 7000 mile oil changes.

 

You can pull the fill plug for the rear diff and look inside with a good light and may be a mirror.

 

Make sure you remove the Fill plug before you remove the drain plug and drain the fluid...I learned that the hard way.

 

Installed a used rear diff with 35,000 miles on it. Only to find out the previous owner had buried the threads of the fill plug, had to remove the diff, and install a new cover and plug.

Edited October 22, 2019 by Max Capacity

Make sure to retorque your lug nuts.

I would also check the rear axles and driveshaft. to do this just jack up the rear end and wiggle the axles in all directions to make sure there is no excess play, with the drive shaft focus your attention to the u joints. I had vibrations at those speeds, but upfront and it turned out to be one of my front axles.

I am in the middle of this right now. I was hoping it was wheel bearings or tire balance issues.

 

It is driveshaft. I am going OEM, but there is an outfit in Texas called Driveshaft Specialists and they can make one that is better with rebuildable U joints in 36hrs at $515 shipped UPS.

So, my mechanic changed out my drive shaft with an OEM one. He said there was a flat spot on the original (160k miles).

 

This oscillating hum has gotten better but is not gone. It is not as loud or as rumbly, but it definitely is still there. He took a stethoscope to the wheel bearings and didn't identify an issue (though not sure if he did it on the lift at 60+mph)

 

What are some next trouble shooting steps? Center differential?

This happened to me recently on my 08 LGT Sedan. I replaced both rear hubs and the noise was still there but much lower in tone, I was so pissed b/c I thought I screwed up something. Before tearing it back apart I took it to a service station and had them run the car while on the lift. Listened to the center diff, tail shaft, rear end and all was normal.

 

I ended up replacing the fronts over the weekend and silence no more humming mine started in around 55MPH and again at 70MPH and when cornering, which is what gave it away. All parts had 194K miles on them, I only use Motul Gear 300 in the drive line so I never suspected the diffs or the gear box but I was sure it was the driveshaft.

May be more cost-effective to start with wheel bearings as the culprit first. They fail like crazy on Subarus.

 

Jack the car up on all four wheels or put it on a lift. Set the car in neutral/park with no handbrake. Grab a spoke of the wheel you suspect has a bad bearing, grab the spring with your other free hand, then spin the wheel as hard as you can, à la Wheel of Fortune. If you feel anything at all in the wheel, you got something wrong. Could be a tie rod, but typically it's the bearings.

 

Driveshaft failure is pretty common on these from what I've heard, but haven't experienced myself.