Hello to the forum my name is Mark and hi to all , I have a 2007 Xtrail Aventura Diesel and I have the most annoying knocking , grating noise and just cannot pin point it , the recent MOT flagged nothing, a mechanic has had the car on a ramp all the suspension , braked , exhaust etc is fine . To describe the best i can it sounds like a dull bell ring sound with the occasion metal to metal grating thats the best I can describe , someone suggested maybe the flywheel etc but it only does it very occasionally and its driving me insane trying to locate it as it only does it when being driven. I do love my little trail its low mileage 75000 serviced each year with good oil etc but this noise is soon annoying . I am unsure if there is any inherent type issues as I have described so any help or advice greatly appreciated , with sincere thanks I am most grateful indeed . 

Hi Mark...welcome to the Forum

Can you say when the noise occurs, e.g. when accelerating or decelerating, turning left or right, in a certain gear?

Cheers,   Trevor