Has anyone have this happen?

Is it an OE diff or has it been replaced with an aftermarket unit?
Have you performed any maintanence on it?
You may need to do a fluid swap. Might also need a LSD additive if its been changed (fluid).

Other than that, unless its a locker, it should be relatively quiet

l owned a 1998 Impreza & with 100,000 miles on the wheels,it was necessary to change rear wheel bearings three times two on the passenger side.
Never a problem with the differential,and l even pulled a trailer(with less than 200 lbs.) on many occasions.
Does ur ''chatter'' become louder as u turn a corner,left or right?
If the answer is yes & it becomes louder one way or the other, that was my sign that yet another wheel bearing had bit the dust.
A Subaru dealer will do it right. They installed the last one,and no subsequent trouble.
The all wheel drive rear end may not be familiar to other mechanics.
l know, with the second change the mechanic needed to call his Subaru contact to get it done.

Sounds like you're asking whether anyone else has experienced a chattering differential. Personally, l haven't. l think what you'd actually like to know is what is wrong & how to fix it.

There r a few possible causes for the chatter, but it is unlikely it is coming from the differential itself. At least, u should hope not as that will be expensive to repair. l will try to debunk the chattering differential diagnosis first.

The most common differential on an Impreza is an open style which seldom requires anything more than an occasional gear-oil change. If the chatter is indeed coming from ur differential, the only possibility is a broken tooth on one of the gears. That will require a completely new differential which dealers & mechanics just LOVE to charge extra for, despite being a relatively easy fix. But in all honesty, that is probably not it. Driveablity would suffer immensely if u lost a tooth. Not to mention a '97 simply is not powerful enough to break gears.

The other differential offered from the factory is a viscous type. The gears spin inside a gooey mass of specially formulated oil. If the oil degrades, the differential effectively behaves like an open type. Again, the only cause for diff chatter would be from a broken tooth. Pray that is not it.

If u have an aftermarket diff, u most likely have a helical type as this was the most popular type available for Subarus. This needs good quality gear-oil on a slightly more frequent basis. But still, the only way to make it chatter is to break a tooth. Same as before, driveability would be poor. The car would wander & skip around even when going straight. Judging from ur relatively low concern, l am guessing that is not happening.

The other aftermarket diff was not popular with Subaru but was available for a short time, so it is not impossible that ur car is fitted with one. It is called the clutch type. Inside, there r several disks of metal & friction material (think brake pads & clutch disks) which spin around. If one of the friction disks were to break, you'd have chatter. Even so, this is an unlikely culprit.

The only way to fix a broken differential is to replace it. A new diff will cost between $800 & 1500 depending on the type. A used open diff will probably sell for around $200. Replacing it yourself will take some time & elbow-grease, but can be done alone using nothing more than a jack, stands, & a big socket-wrench. Power tools & a lift will save ur time & energy, The alternative is to take it to a mechanic who will charge ur $1000 for the part & anywhere from $300 to $1000 for the labor.

As Chris said, the most likely cause is bad wheel bearings. Sadly, this hard to repair part tends to break quite often on Subarus. One big symptom is the chatter is more noticeable when u turn one way than the other. For example, as u turn left, u place more weight on the outside wheel which strains the right bearing, leading to chatter. You will know for sure when all of the grease has completely leaked from the bearing & ur chatter turns into a squeal.

Chris is right again. Unless u want to attempt to fix it yourself (check out the big link at the bottom), u should take it to an experienced Subaru technician either at a dealership or a known specialist. AWD vehicles require some specialized tools & know-how & not all shops have the skills or resources.

Another possibility is a screw or nail in the sidewall of ur tire. If the object is lodged where the contact patch meets the sidewall, it will be silent on straightaways, but as u turn & the tire warps, the object will strike the ground & create a chattering sensation. Go over ur tires as closely as u can in bright sunlight to find the screw. Bright light helps as the light will glint off exposed metal.

One more possibility is worn out bushings. Subaru rear differentials r suspended using a series of rubber bushings & metal braces. Even with fresh bushing, when u accelerate hard, the diff will clunk as the diff case rotates & slaps against the trunk floor. Imagine if all the bushings were to get worn our & go soft. Then the diff case will wobble around as the differential tries to do its job of transferring torque from one side to the other. The case will rattle in place & create a chattering noise. To fix the problem, u will need to replace the bushings, but since it is really not going to harm the car, u could just leave it alone & get used to the noise.

Join the forums. You will find great information from knowledgeable die-hard Subaru fans.

OMG! What long to a short question.

Unfortunately, they r all wrong. 1997 Subaru rear diffs do not break. This is what it is.either u just put 2 new tires on either the front or back..and they do not match the other 2.. or u have the AT Temp light flashing on the dash when u start the car...which is telling u that u have a bad rear speed sensor on the back of the tranny.

Your tranny is binding. It feels like its coming from the rear diff when u turn, because those wheels can not move at different speeds when u turn. Have u ever had a 4WD truck in 4X4 mode.it binds when u turn tight. This is what is happening. There r front & rear speed sensors that control the rear drive part of the tranny. The tranny applies & releases clutches in the back of the tranny that r mounted in a sun gear.

You could have a bad apply solenoid located in the back of the tranny also.

Check ur tires first.they must ALL MATCH!! If they do, take it to a Subaru mechanic & have them run the other tests.