My 2018 outback is...

First have the car checked out at a decent garage to determine if in fact the noise is tire related vs a bearing or other driveline component. Any decent name brand tire will work, can I assume yours are worn and old? Check out tire rack.com they have reviews. Enter your vehicle info and search under your tire size. I personally would recommend, Continental, Michelin, Good year and or Firestone.

ubarus have had soft rear wheel bearings for decades. The opportunity to use bigger, sturdier ones when the geometry opened up to 4 1/4" spacing in 2015 was NOT taken advantage of, with the result that rear bearings in 2015+ wear even more quickly than before! Be sure to use a stethoscope up on a lift while rolling to determine left from right side, as they do NOT wear in pairs; usually the right rear wears first. It is VERY unlikely that the noise is from the diff or axles themselves. However, if your rear tires are lumpy from lack of rotation then you'll get a somewhat similar noise. The OE Bridgestone Duelers are famous for getting noisy well before wearing tread out. Having a rear passenger guess which side bearing is noisy is only a way to result in an argument after your naive wrench replaces the wrong side, so use that stethoscope. Owners of 2010- 2014 CVTs that wear out may present a similar bearing noise from the FRONT, where differential diagnosis of the source being a FRONT wheel bearing or the CVT is warranted. So far I haven;t had issues with the dozens of 2016-2019 OBs I've sold. The rear wheel bearing assemblies are now cheap, but removing the seemingly-fused OE can require much brute force...or even removal of the entire spindle to press out. Some just pop off with a hammer blow, some require a fabricated pry-bar extension. Figure 1-3 hrs for the job, as it is NOT DIY! Note that rear brake pads are a bit thin and may wear before the fronts, so padding the rear isn't a bad idea if you're back there anyway...but only if really thin. To vastly improve handling (reduced understeer) and lessen body roll and yaw it's a grewat idea to install Subaru's STi 20mm rear swaybar while you're back there. Cheap and remarkably effective. Further, if yours is a 17" wheel Premium with shitty 225/65 rubber, you'll improve handling significantly by changing to 225/60R17 rubber when tires are needed (of course do all 4 as a set when changing size). Limitreds with 225/60R18 are already better in this regard, but gain improvement by similarly stiffening to 225/55R18. 35F/32R psi s a good target. Have fun, be safe and wear a mask, eh?