The car is over in at my dads shop. I don't have time to drive out and work on it after work. The car is not being driven though so this weekend when I have time I'm going there.
Sorry man, I bet it's no fun at all. Hope it's something simple and cheap. I listened on two devices, but it sounds different on each, though I lean more towards a tap than a knock. Fingers crossed for you.
My intended point was just to let yourself off the hook and check it out.