1954 BMW R67/2 with Steib S350

Idle after ride home on a cold night. Note piston rattle on right cylinder. Rattle has been there since I had the bike (about 8 years and 5600 miles) without perceptible change. Rattle is accentuated in closed garage, but I took this vid to share the rattle and get opinions. One phenomenon to note is that the idle normally isn't this fast, but consistly is like this after a 15+ minute ride on a cold (40'F) night. Here in Namibia is high desert and the bike is operated at about 1800 meters above sea level.