When I have driven for about 20 minutes, the moment I turn left or right , a knocking sound starts up towards the bottom back of my car. And the longer distance or driving on the freeway at 60mph, it starts to quicker and is more constant and louder. Now when I press the brakes, it stops knocking. But if I let up the gas without the brakes, it still knocks. My friend has checked everything and can’t find the problem