at 45 mph sounds like a marble is in my engine on 2006 BMW 325i

When I reach 45 mph I hear a rattle in the engine that sounds like a marble. But when I am sitting still and rev the engine it does not happen? 150 thousand miles on car.

1 answer
When sitting still and revving there is no load (or little) on the engine and transmission, also ignition timing problems (they are computer controlled) can also cause a rattling under load. At CarMasters we depending on the problem can install a electronic chassis ear on vehicle during road test or operate on a lift with one technician under vehicle listening while and other is operating the engine and throttle from drivers seat to identify the source of noise/concern