On my 2001 ML 320, the charging syst. indicator lamp on the dash lights up when I go down an incline in a parking garage, then returns to normal - unlit, during any other driving conditions. Battery is 2 years old, cables & connections are tight & clean. All cells have proper acid level. It sits tight in the box. No signs of arcing from any connections. Belt looks good. No unusual noise from the alternator. I've looked at all of the obvious possibilities-- maybe. Any ideas? Thanks