This is exactly the problem i had.. I brought a new bonnet, took the hinge of, refitted it and seemed ok, Mabey its prone to coming loose? Try taking it off cleaning it up, wee bit of grease and refit.
I remember having this same problem for a long time and couldn't find what it was! I finally discovered that the hood bends slightly from slamming it or dropping it to close and the back of it hungs lower than what it should. The fix is to bend the hood backwards to where it sits properly. The way to do it is to put one hand at the front of it and the other at the middle across each side (one side at a time) and try to bend the mid section upwards! Dont force it too much cause they are as hard as butter! Hope what I describe makes sence to you!