I have a 2008 Volvo S40 with 11,000 miles on it. Over the last 3,000 miles it has developed an odd noise coming from the tires I think. When driving slow(under 20mph) it sounds like a wah wah wah wah wah sound as you coast along. It gets faster as you pick up speed till the sound is seemless. My tires are balanced and rotated every 5,000 miles. Wear seems normal. Sounds like road noise but goes up and down in pitch. Any idea on what this sound might be before I call the dealer?