Not sure why you would get a squeal when you turn from the rear diff. I have had a rear diff whine since I got my truck 2/14/2004. It is most noticeable without the radio on between 60 and 67 mph. Slower than that it is more muted, after 68 mph it is gone. I've got the PML cover and have used 75W140 since 5,000 miles. I've taken off the diff cover a few times, and see no evidence of excess wear on any of the gear teeth. I took a photo of the gears last time I took it off, but it says it is too big to post here.