Re: Front end whinning then grinding
Some metal flakes is not a good sign, it came from somewhere. If it was really just a few pieces, its probably not that bad though. When opening the diff, all you can see a re the ring and pinion gear, the bearings you can't see that good and only when they have a lot of play you will discover it.
Why did you change the U-joint, did it have play on it? You could remove the front propeller shaft, drive around a bit and see it the noise changed. If not, you have a good change that a CV joint is bad. But normally whinning comes from the diff.