Peculiar rattle?
Srangelove does the noise appear to be more noticeable when the engines and transmission are hot, or noticeable at all when cold.
The analogy of transmission gears chattering due to uneven idle is very sound, even with a well set-up fuel injection system (balanced etc) at normal idle speeds it would not be unusual to hear some internal noises.
When you pull the clutch in you would be loading the release bearing, however; there are cases where the release bearing can be noisy under load and no noise off load and vice-versa.
You are best advised to get someone that knows their stuff to take a listen, and at the same time try to have a listen to someone elses Boxer engine and come to your own conclusions.
15000 miles is nothing to a release bearing and I doubt that you have a problem in this area unless you tend to sit in traffic for long periods with the clutch dis-engaged - this would most certainly cause the bearing to develop a fair amount of heat and then the lubricant would literaly centrifuge out of the bearings body.
The clutch cush drive could possibly be suffering from worn springs and this will produce a noise in the same way that you describe....but hell its difficult to be positive with a diagnosis done at a distance.....do the previous option and get A.N. Other to have alisten.
Oooh! Even a BMW dealer might listen for 'gratis' try your luck.
Hope that it is just the normal everyday noise, good luck..again!
