My wifes car, 2007 RAV4 limited, 2.4L 4cylinder just started doing the same thing. It is not engine speed related, but vehicle speed. I also got the sound to go on and off by moving 2-3 feet. It just increased the on-off frequency when you travel faster. I can sit in one place, have it in neutral and gun the engine with no affect. It only happens when the car is moving. It is almost like a square wave of turning on and off, when you get going fast enough it is like it almost gets better. I don't know if she has ASL. I will look for it. Any other suggestions out there?