I have a 2000 Ford Explorer XLT, 59000 miles. I bought this car a couple of years ago used with 36000 miles. During the test drive the salesman pointed out that there were new tires and therefore the " road noise". The " noise" has continued to get louder and recently, while considering to trade it in on something else, the dealer mechanic commented on the " unknown" noise in the front end while test driving it. Now, we are concerned since it is obviously not " road noise". There is no shimmy or bumping, just rotational noise insink with the speed of the tires and it gets a lot louder if you are using 4 wheel drive. We need to go on a long trip and now I am concerned about the " worthiness" of the vehicle. Any ideas?