Hey Scotty my brothers Subaru legacy rear differential is making noise as he drives. I hear rumbling/noise in the back as he drives. He thought it was the tires so he changed them and made no difference. I ask him if he changed the fluid he said no. Is it damaged or is there a chance he’s lucky and just try changing it. He had bought it in 2017-18 with 30k original miles For 10k. Thanks appreciate it.
According to the Subaru manual (I was only able to find the Canadian one) you should have inspected the differential fluid every 6.25k mile service and replace that fluid at 62.5k and 125k miles.
Perform that procedure now - it may help, but it may be just mechanically worn from lack of service.
Get it on a lift, inspect the AWD drivetrain, inspect and adjust differential fluid.
Are you sure it's not a rear wheel bearing? A friend had a noise like that in back of a 2017 Outback and it turned out to be a bad wheel bearing.
