In January I purchased a front wheel drive 2010 Toyota Highlander with 23,000 miles. When driving just over 60 mph, there is a fairly loud humming sound from the back of the car (seems to be more on the right rear). The dealership replaced the left rear wheel bearing and performed road force balancing on the new Yokohama Geolander tires. The annoying hum is just the same. Please advise. Thanks!