noise sounds like I have a flat spot or something in my tire (sumitomo HTRZ's). when I get up speed it almost sounds like a helicopter. I ruled out the engine because it made the sound on the highway while in neutral. I checked my tire pressure and the tires only have about 4k on them. The sound definately slows down with speed. My car had been sitting for 4 1/2 months, but I thought with todays tire technology flat spots were not that common. I check the tires and they looked ok but I was told a steel belt could have shifted while sitting on the concrete. Any ideas?