There are "hydraulic elements" in the ball studs, which push up and hold the rocker against the cam. If they get weak, they don't hold it tight enough and you get a click.

It could also be a worn rocker arm or cam lobe. Best attend to it while it is still possibly a cheap repair.

__________________
Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe