There is a grinding noise coming from the differential area when I'm on the highway.
It sound like your differential may be failing. There are many bearings and gears in the differential that may be damaged. A technician can use a stethoscope to pinpoint where the noise is coming from and determine if it is in fact the differential. I would recommend having a technician come out and inspect the noise that you are hearing and drain the fluid and locate any metal shavings. If metal shavings are found the differential probably needs rebuilt or replaced.
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