jbeditor

I have a sound that occurs when I drive that is only audible in the cabin. It's a low drone at slow speeds and it gets progressively higher in pitch the faster I go. Although there are no abnormal vibrations present, initially I thought it was related to my suspension/tires/wheels/bearings as it sounds similar to tire noise from a large knobby tire. After many visits to my usually reliable tire specialist, who verified all wheels being true and no mechanical anomoly's, and replaced all 4 tires (Michelin Pilot Sport from BF Goodrich), his only other idea was that it could be the resonator. I don't know how the resonator operates, but what he explained to me is that it regulates the sound of the car in some way. I cannot hear the sound when I am in neutral either driving or in park, no matter how high I rev the engine. I trust his judgement, but I'm not sure I understand how the sound is related to the muffler system, but can't be heard unless the car is moving (in or out of gear). My question is whether or not anyone has had an experience similar to mine?