Had exactly the same symptoms and only found out what it was the first time I removed the LHS radiator side cover. It was the top one of the two set screws that join the panel to the exhaust heat shield. The screw is too long and tapped against the exhaust pipe, it had actually worn away at an angle. I cut off about 7-8mm, refitted and the rattle disappeared!



Try pushing on the screw head and see if it makes contact with the exhaust with a metallic tap...

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