Re: 80 mph rear end noise and the dealer
I would take it to the dealer. Your not happy with your car as is. I think before they start a part by part tear down you will more likely get a new replacement 3rd member unit & be on your way. May take some insistance on your part if any band-aid adjustments they try don't work but hang in there & be moderately forceful. Good luck.
Crossfireone