I have a 2001 Subaru Outback Wagon (128,725 miles) that makes a “thunking” noise when making a hard turn to the right or to the left. I only notice the sound at low speeds (1-10 mph), but I haven’t taken the car to an empty parking lot to see if it would make the sound at higher speeds. It also makes the sound in reverse. I had the front right axle replaced in attempt to correct the sound (appeared to come from the front right of the car), but to no avail and $200 later . . . For periods of time the car won’t make the “thunking” noise . . . but then it will start up again. I read something about an issue with the steering hydraulics in 96-2000 Outbacks being the problem (Technical Service Bulletin TSB 04-09-01), but I am not yet convinced. Hoping to hear if some one else has had a similar problem and identified a solution.
With that many miles on the vehicle, the thing to have checked are the ball joints.
Tester
If this an automatic version you can look up how to temporarily disable the AWD(involves putting fuse in or pulling it, cannot recall).
If you disable the AWD and it stops it likely is your clutch pack.
Another major question, do all four tires match in tread depth, make, model and size? Have they always during your ownership?
I think andrew j is on the right track. If your Outback has an automatic transmission, insert a fuse into the FWD receptacle under the hood (the owner’s manual will tell you where it is), and see if the noise goes away.
The transfer valve and clutch pack in the rear of a Subaru automatic transmission control drive to the rear axle. When the valve and/or clutch pack wears (this is a wear item, and your car has enough miles) the default mode is DRIVE, and you can get binding in the AWD system during tight turns.
The only cure for this is to replace the valve and clutch pack. I paid about $750 for this a few years ago.
There are other possibilities, but the noise you describe and the conditions under which it occurs are classic symptoms of a worn transfer valve and clutch pack.
Non-matching tires can accelerate wear on these components, which is why andrew j asked about the tires.
If your car has a manual transmission, try having the transmission and differential lubricants replaced (both differentials). This might solve the problem.
All four tires match in tread, make, model and size . . . and they always have!
It is a manual transmission . . .
I’ll see if the changing the lubricants makes a difference. . .
This seems to be right-on-the-money! I’ve been having the problem described (with a 1998 Subaru Forester). My mechanic advised changing the lubricant in the rear differential. The first time I did it, it seemed to help. I’ve done it twice since, and the noise continued. After finding this page and discussion, I inserted a fuse in the receptacle to change from AWD to FWD; AND THE NOISE WENT AWAY!!! I might just continue this way and forget about AWD (at least until I can afford the fix).