I recently bought a used 2004 Auto subaru legacy Bp5 about 3 months ago. However, I have been hearing a pulsating whummmmm whummmmm whummmm noise but ONLY when i hit 60kph. The noise is also a vibration that i can feel through the gas pedal and the floor. It pulsates and is not a constant noise like a bad wheel bearing. Also, the noise increases its frequency as the speed increases. Anyways, I have taken it to several  mechanics and neither could figure out what the noise was because it only happens under load. One mechanic said it was probably my differential starting to fail. The other said it could be a lot of things and that i would just have to let it get worse. I can't wait.....its annoying and I dont want it to get worse and cause any more problems. The noise doesnt change when i turn, as long as i am going above 60kph, the noise is there. the noise also increases with speed, or pulsates faster when i speed up, slower when i slow down,even in neutral. Any ideas???? I would really appreciate any input. Thanks!

Edited July 30, 201411 yr by KIGO254

see if there is any change if you swap tires front to back. Good opportunity to inspect the tires, brakes and other gear too.

 

you do understand the tires must be the same size;  as in, same brand/model/size and even wear-level within 2-3-4 or so  32nds/inch right? bad for the AWD system if not.

Edited July 30, 201411 yr by 1 Lucky Texan

i replaced the tires two months ago and they are similar in every aspect,bakes are okay.Noticed previous owner had one disimilar tire.

was the problem you have now present before the tire change?

 

if the car was operated with a dissimilar tire on dry pavement, that could cause problems due to 'torque bind' and portions of the drivetrain could have suffered from too much stress build-up.

 

Will the care idle through tight turns on dry paved surfaces without jerking or bucking? There should be a FWD fuse position inside the fuse box. You can insert a spare fuse of any amperage and see if the problem goes away. Other componenets to inspect would be u-joints, carrier bearing and axles I guess.

 

(Subaru wants all 4 tires within 1/4" [7mm ?] CIRCUMFERENCE of each other)

Edited July 30, 201411 yr by 1 Lucky Texan

The problem was present before the tire change since i suspected the tires were the cause of the problem.On tight turns the noise is still present.Will inspect the

u-joints, carrier bearing and axles soon as i have some free time.

only a noise? no 'jerkiness'/vibration felt, right? Also, if you were to coast in neutral, would the sound change?

The noise seems to increase in intensity over time,4 weeks ago it was barely audible.Now it can be heard even when the radio is on .Vibration is felt on the floor.

At neutral the noise is still present, but I have not tried disabling the AWD using the spare fuse.

Edited July 30, 201411 yr by KIGO254

Wheel bearing. The noise will oscillate if the inner race is worn as the worn surface rolls past the loaded rollers, which will only occur for about 1/3 rotation of the wheel.

 

Also if multiple bearings are noisy the frequencies can cancel each other and cause a "helicopter" effect.

 

Get a shop to put a chassis ear kit on it and drive it. Often the bearings in these do not exhibit any looseness until they are severely worn. They can make noise for tens of thousands of miles with no signs of play.

Edited July 30, 201411 yr by Fairtax4me

soob bearings are variable as to exhibiting typical failure modes but, it's worth trying the 12-6 o'clock rocking test.  I found a bad bearing on my WRX that way. Compare it to its mate. My bad rear bearing moved maybe only 2mm or less. The other side didn't move at all.

 

maybe use an infrared thermometer to check temps in case one bearing is consistently 40-50 degrees hotter than it's mate.