Thanks guys, right. Update... Not a huge amount of room on the other side of that metal plate and its heavy! I took all the bolts completely out just to have a good look underneath before I then tightened everything back up. I used the old bolts, I have the TTT bolts on order from BMW and top nuts... soon as they come in I will fit them. So its stopped the knocking. I have a torque wrench. torqued them to the correct setting then gave it another quarter turn. Then another quarter turn to be safe . I did it at the weekend and have only covered about 30 miles since, but it has been totally silent. Only time will tell if it comes back again. WARNING... the metal plate is heavy.... I put a bottle jack and a piece of 4x2 and then lowered it off. I would estimate 5kgs but I am sure someone on here knows the exact weight. I would say as I was on my back under the car with only one hand free, if it came loose when I was undoing the bolts it would hurt a lot. So careful.