I have a 2005 Hyundai Sonata with the larger 6 cyclinder. It seems that when highway driving more than a few minutes, my car knocks from deep inside the car. I have noticed it going up hills also. It seems to get louder and more frequent the longer you drive it. It is not a gas issue. Sometimes when the knock is loud, you feel it in the gas petal. I have had it services by Hyundai twice with no avail to fixing it. The service technician even took a ride with me to hear the noise. They have replaced the water pump, changed the oil and tightened a loose bolt. And I am getting near the end of my 60,000 warranty. Help please.