My 05 Mariner (2.3L 2WD 49,000 miles) makes a humming noise. The faster you go the higher the pitch. Sometimes there's a woo-woo-woo-woo sound to it. I've heard that the original Continental tires are to blame. The tires still have plenty of tread left. Anyone else have this problem? Did new tires fix it? Could it be a bearing problem? It's been going on since 20-something thousand miles. If it was a bearing something would have broken by now, right?