Need E-450 rear axle repair in Seattle area

I think I have some noise that sounds a lot like tires singing; however, I've about convinced myself that it isn't the tires since the sound is from the rear and I have the same tires all around. No vibrations at all. I've cleaned metal off of the fill plug magnet several times in the last 10K. It'll build up to about 1/16" thick on the magnet. I've got powder, small glitter, and some black flakes that don't look like metal but they are magnetic. I'm in Lynnwood, just barely. Probably 2-3 miles from Randy's which I also drove by almost everyday before I retired.