Whenever driving at higher speeds, the bonnet/hood trembles very hard, even on a flat surface. I really can't find out what is causing it, checked the metal connections and have made sure it is correctly closed, lubricated. From the moment the speed drops below 140km/hour it does not move and is perfectly still. I know it is not normal because I had 3 XJ's before and none of the hoods trembled. I only have this Jag for less than 2 months know and have no ideas left. It seems to be caused by air but I can not figure out where from. When my wife drives, she is afraid the entire car might take off.
Anyone any ideas? Thanks in advance!

 

Did you check that the bonnet hinges (at the front) are tight? Another possibility is that your engine mounts are shot allowing one side of the engine to lift up under higher stress (higher speeds) and contact the underside of the bonnet.

 

Thank you. Checked the hinges but now a part of the undertray seems to be missing. Will get a new one and see if that fixes it.