Diff noise

Hi, new member here with a problem that has probably already raised its ugly head.
my MPS 6 has developed a whining noise in the front diff area. Starts at about 40 km/h and is definitely annoying.
Have been told by Mazda that they don’t support parts for this model and have been trying various wreckers that they can’t help either.
Does anyone have a solution or am I going to have to pension the old girl off?
Have checked oil levels etc , all seems ok
is there any particular oil for the transfer case that helps with the noise level?
Any help or advise will be appreciated

Andrew Holley
Dubbo