I get a pretty noticeable whirring noise from the rear of my car, trying to figure out if it's wheel bearings, crap tires, or just 20 year old subaru noises. What should I be looking for? Gas mileage is bad, but that's probably because I have to redline to stay with other cars

you could take some temp measurements with a remote infrared thermometer.

 

Also, lift the rear of the car and try rocking the tire up-down. (12 to 6 O'clock) comapre both sides. really should be zero movement. i gad a bad rear bearing that moved about 2mm, other side was rock solid.

 

you can also compare sound with a mechanics stethoscope from side to side - might hear rough bearings.

you could take some temp measurements with a remote infrared thermometer.

 

Also, lift the rear of the car and try rocking the tire up-down. (12 to 6 O'clock) comapre both sides. really should be zero movement. i gad a bad rear bearing that moved about 2mm, other side was rock solid.

 

you can also compare sound with a mechanics stethoscope from side to side - might hear rough bearings.

Would temp measurement not be diluted by brake heat? Not meaning to doubt, just understand

wheel bearings are nearly impossible to diagnose sometimes - they can (not will, but can) pass every conceivable test known to man.

bottom line - there is no definitive test for bad wheels bearings on the vehicle.

 

suggestions:

 

ride in the back - if it's notably on one side - then it's likely wheel bearings.

rotate tires and see if the noise moves.

 

temp gun will isolate some.  yes brake heat is present but a bad enough bearing may heat the hub up as well after a long drive - that side can be heated more than the other.  does it always work - definitely not. but if one side is notably 50 - 100 degrees hotter, that's your man assuming the brakes are working properly.

 

mechanics stethoscope - sometimes turning the wheel by hand and listening around the hub or strut springs will pick up noises.  does it always work - definitely not.

 

grabbing the tire and checking for play - I've never seen one fail that test.  i've never seen a difficult to assess wheel bearing (and i just looked at one this past weekend) have play on the vehicle.  i've seen them be showroom tight and then be all sorts of play once the hub was off the vehicle though.

Yeah, chased a bad rear wheel bearing myself.

 

Had the noise, just couldn't pin-point the "where it's coming from" part, even riding in the backseat.

Didn't seem to change any doing corners or curves in the road.

 

Didn't "notice" any play in the wheel trying the wiggle method either.

 

New bearing installed on passenger side, noise gone. Had 2 Members here for a visit, and they said it sounded like that side.

 

If you loosen the axle nut, you loose the bearing pre-load, so don't do that during any checks you make.

 

I even went so far as to remove the driveshaft, one section at a time. Rear half-shafts, one at a time. Just to eliminate any possible causes in my search.

 

Old ears make it difficult to pin-point noises at times.

This is making me lean towards just buying the hubs and wheel bearings and doing them. The entire assembly is apparently from a junked 95 legacy, so even if they're not the cause I feel like they will be in a short while. I just can't get those 13 mm bolts off.