Hello All,

I had my front and rear differential oil changed back in late October from a lube place and bill of sale states that they used synthetic oil but the additive was not on there.
In January it started to make like a rubber grinding noise when I started to turn from a full stop. Don't know what this is.
Took it to another mechanic and he advise that it is the LS (possitrac) and possibly the addititive was not added as it was not on the Bill of Service....he added the addititve and it pretty well stopped it but it is doing it again???

2006 Ford F150 5.4L 4x4

Any advise.

Sam