Hi all,

I'm hoping someone can help me pinpoint this problem, as my local trusted mechanic and stealership keep telling me inconclusive and conflicting things about what I'm hearing and what I need to have fixed.

About 4-5 months ago, I started hearing this humming noise that seems to come from the front of my car (hard to be more specific) when my '02 WRX is accelerating, around ~3000 RPM in 4th or 5th gear. The noise will ramp up in pitch as the car goes faster. The noise goes away when I let up on the pedal, and also goes away if the car is in neutral. It only happens once the car has been on for a while (so, whatever is the culprit needs to warm up some before the sound is made).

The noise has not gotten louder since then, but has not gone away either.

My local car shop put it up on their lift and tried to get it to make the noise to no avail (hence why I know it must be under load in order for the sound to be made). They tell me it's probably something to do with the axle or CV joint, or maybe a wheel bearing. My local dealership tells me that I've been driving it too hard and it's probably the turbo going bad. I'm thinking to myself with my limited knowledge, and by searching around on the forums that it might be the transmission/front differential.

Can I get some input on perhaps what I should try to narrow down possibilities? Any one have ideas on what I should check? Any help is greatly appreciated.

2002 WRX, purchased August 2001, 155000 miles.

 

This seems counter-intuitive, but the problem is your rear differential. Trust me, my dealer swapped out the center one twice with no results, but then did the rear one and it fixed the humming noise. Check the rear differential, I'm serious!

 

Did they tell you what was wrong with it? Low fluid levels? Busted gears? I'm obviously long out of warranty and I can't just ask them to go around replacing stuff on my dime...

 

It was "bad" in general, bearings, teeth, the works. They didn't rebuild it, they swapped it out. I don't know any way to check and see if that was really the cause without actually taking the differential off and looking inside. However, I had the exact symptoms you were describing here: a loud humming sound under acceleration, especially in 3rd and 4th gear on the highway. It went away when you let off the gas, and it at one point was such a loud hum/groan that I could hear it with the factory radio set to 10. The hum comes from "play" in the rear driveshaft as it enters the differential, from what I understood.

A wheel bearing tends to "pulse" when it makes noise (uneven wear makes it go squeak-squeak-squeak with a pause between each) so that probably is not it. A bad CV joint or axle would also be bad when just rolling (neutral or off throttle). I wouldn't be completely convinced that the differential is your problem unless I could hear it for myself, but I do think it is worth checking out.

Here is my original thread from back in 2005, when I noticed the problem:

https://www.i-club.com/forums/engine-power-ej20t-pre-2006-wrx-jdm-60/loud-hum-whoosh-50mph-86517/

 

A bad pinion bearing will completely destroy the differential. Try using a mechanics stethoscope(bad spelling) to pin point the sound in the differential. You can also trying pushing up on the driveshaft where it goes into the rear diff. If theres any movement the pinion bearing is bad.