Hmmm, could you explain what part exactly is the headlight bucket and the lock cylinder?

Well, guys, I still havent found the root of the evil knock... BUT!!! I noticed that under the tank there is a small rubber grommet, cube shaped. Not the one at the front, it is about in the middle of the tank, between it and the frame. The thing is that its only at the right side, on the left side there is no rubbery cube... Anyone know if we are supposed to have both of them instead of one?