mtvp

Now a little on the back story. I purchased a Cayenne from a dealer that had 17,500 miles on it. I have a little information from the Dealer . Who said they had two tires replaced before my purchase. The lease driver before me had a tire issues so they changed the front two. I'm not sure about the mileage and the Dealership is not forth coming with more information.
I now have put 6K on it over the last seven months. There is 23K on it and the howling noise from the underside is more than tire wear. At least that is the second opinion that was shared with me from a independent shop. That I had stopped in to have him rotate the tires. He declined to rotate them after he drove the vehicle. He did not think it was tire noise and that it would be better if he did nothing Being that it was still under warranty. I should see my local Porsche Dealership. He told me that the old tires and the new have 6/32 difference in them. I would have to believe that at some point the tires were rotated once or twice. One tire is now approaching the wear bars.
Would that be enough to cause this kind of trouble ? Front transfer case bearing noise?
Should all the tires have been changed at one time? Did the selling Dealer not step up?
Well , any opinions will be read , and thank you .