I posted about this a while back in the EJ20 forum, but now I have localized the problem and I'd appreciate some more input on what is going on...

I have an 02 WRX with 30,000 miles. When I approach 50 MPH in 3rd or 4rth gear (3500 or 2900 RPM) I can hear a very loud humming sound that seems to come from near the engine compartment. The sound only appears when I am accelerating; if I step off the gas, it goes away.

Here's what makes me think my transmission is involved: if I push in the clutch, the sound goes away, even if I do not change speed at all.

I took it to my dealership (a very reliable and knowledgeable bunch, they are even fine with many mods) and they couldn't figure it out; they said it might be my aftermarket tires and rims ("17s). But the fact that depressing the clutch makes the sound go away focuses my attention on the drivetrain. Any clues?

 

I'd be surprised if any humming coming from the transmission itself didn't manifest itself as something rather obvious quickly. I'd be more inclined to think it's a wheel bearing. You don't get the sound in 5th gear at that speed though?

 

No, only in 4th gear at 2800-3000 RPM, period.

Hmm, a wheel bearing? That sounds like a pretty good guess -- but I still can't explain why pushing in the clutch makes the sound go away. It certainly left the techs at the dealership puzzled, and some of those guys have been working on Subarus for 15+ years... I agree that if I had a transmission problem I should probably be having other symptoms, such as a slipping clutch or grinding between shifts (I don't).

I originally thought it was an exhaust leak -- perhaps the thing with the clutch puts that idea back in play?

 

this a common problem wrx transmissions..the first step you should take is replace yous trans oil..1 reason they start to whine or humm is cause the oil is beat it should be replaced every 15000 miles so you should have done it twice ..andther reason it would whine is if it was grinding and scared the gears but if it never grinds all you should have to do is replace the trans oil..ur dealer should have it or any of these vendors should carry what you need.............

 

No, the fluid was changed by the dealership and it actually made the sound louder! Also, it never grinds, except for the common grind while downshifting into first. Thanks for your input!

 

I never grind going into first, but then agian I have had a WRX sense the first month they came out so I learned quick heh. Heal toe downshifting.. always(especialy when going into first)

Your Sancros will luv you!

 

try an aftermarket oil thats a little thicker than stock then ..like the royal purple ..ive only heard good stuff about it ... give it a try its alot cheaper than another tranny ya know...

 

If you're trying to suggest the first-gear grind is a user-error issue, you couldn't be more wrong. Not only was I one of the first WRX owners in Arizona, but I have been driving manual transmissions since I was 16 (BMW 2002, VW Rabbit, BMW 320i, Porsche 911, Isuzu Trooper II, just to name a few of my past MT cars) -- I know how to shift into 1st from a roll. The slight grind when downshifting to 1st while rolling is a known and common issue with the WRX 5MT; do a search of the forum and you will find hundreds of posts about it.

 

I may try the shockproof oil, but since the factory fluid in the tranny is totally fresh I might give it a few thousand miles to break in first and see what happens. As I remember, when I first bought the car I was pretty unhappy with the inconsistent and picky shifting for the first 3000 miles or so (and yes, I did drive gently during break-in). I still have 6,000 miles left in my drivetrain warranty, so I will probably take it into the shop again and see if I can get them to swap out some parts...

 

I get the sound in 4th too on my 02 RS. I can't hear it as much when accellerating, but when I let off the gas in 4th at about 2500-3000rpm I get this rattly grindy type of sound.