1999 Subaru Legacy - Whining Sound

I have a 1999 Subaru Legacy 2.5 GT and I get a whining noise that is directly proportional to road speed when I drive. The noise is ONLY heard when the car is moving and your foot is on the gas. The second you lift your foot to coast the whining stops. If you are stopped, no whine. If you change gears, the frequency of the whine doesn’t change. Turning the wheel left/right doesn’t change anything. If it sounds like anything I’ve heard, it sounds like a dry differential. I’ve checked the front diff fluid level (the whine comes from the front) and the fluid level is full.

When did you get your last set of tires?

Is this a manual or automatic transmission? I ask because the automatics have 2 dipsticks and just wanted to make sure you’re checking the hypoid oil and not the ATF.

  1. Tires, less than 15,000 miles ago, a good set of Michelins with 2/3 of their tread left. The noise sounds sheet-metal like, not tire-like.

  2. Automatic transmission. I’ve checked BOTH dipsticks. The one for the diff was a real challenge to find.

Thanks for clarifying the part about the transmission type. What has happened many times is that someone will mistakenly drain the hypoid oil from the transaxle by mistake while performing an engine oil change so I just wanted to make sure the hypoid oil is fine.
Yes, they kind of hide that little stick down there out of sight and out of mind.

Unfortunately, what you’re describing sounds like a differential whine. Thats’s unusal unless the car has suffered an oil change incident or it has very high miles on it.
There is no cheap way of curing this problem as it would involve a complete transaxle teardown and rebuild.
The cost of the parts is high enough much less factoring in who you would have peform this job. Doing this on a Subaru is highly technical in nature (much more complicated than say a normal ring/pinion job on a rear drive vehicle) and requires a number of special factory tools.

If you were at the point of not being able to put up with the noise anymore the best and cheapest option would be to find another transaxle.

Thanks, ok4450, can I confirm that if it is a ring and pinion whine, then it is driveable with no safety issues?

As long as the hypoid oil is full it should go for a long time with no safety issues. The only problem would be having to listen to the whine.