I'm getting a strange sound that I can barely hear while cruising but that gets louder as I accelerate - not as I go faster speed but as I speed up no matter what speed I'm traveling at to begin with. In other words if I'm cruising at 65mph I can't hear it but if I go from 45 to 65 I can hear it. I thought it was an exhaust leak so I took it to the dealer and they checked it and said no leaks. I thought it might be some valve train noise but I had my wife rev the engine to different RPM's and I couldn't hear anything with my head in the engine bay. Just looking for some thoughts and ideas. Thanks.