The Moto-Guzzi Nuovo Falcone VOC

Hi,  my Military NF has now has 17000km plus on the odo. I’ve ridden it  it for 15000 Of those and enjoyed them all. It has always had noisy valve gear. It makes a “clacking” noise, most noticeable at tick over. If I operate the valve lifter very gently, so that I can just feel the rocker operating, the noise goes quiet. I’ve had the head refurbished by the Cylinder Head Shop, with new guides and lead free exhaust seat fitted. I’ve replaced the camshaft bushes and the rocker spindle bushes , although none of them were badly worn. The cams and followers look perfect. The rocker tips look fine, with no wear groove.  I use 0.15 exhaust and 0.1 inlet clearance.  Any thoughts on a possible cure? It would be nice to ride without earplugs.