I started my car today after it sat for a day and I can definitely hear the sound. I do not think this is normal as the sound was not there before. Something must have worn over time for this to develop and I am afraid it will develop into something more serious down the line as Mike said. Would be nice to be able to get to the source on this as I plan to keep the car for a long long time.
From a few members posted above, it seem that the sound is fixed when the vanos cam gears are changed. So I am assuming that's the source of the sound? Looking at some of the pictures of the s65 builts and the service manual on adjusting the timing on these engines, it seem that the timing is only locked by the tension on that one bolt going through the cam gears into the camshaft. Can some folks that have worked on this engine confirm? If that's the case, would this rattle over time risk knocking the timing off on the engine? The sound is very loud and violent if I let the car sit for 2 or more days.
For the time being, just mean I have to drive it every day!