BMW Repair: 1998 328i fault code #6, emmission control, vacuum leak

Question
I read an article about 4 months ago in the local car club newsletter. It was about part of the emmission control system which has a seal that begins to leak after aging.  The result is a whistling or whirring noice (sounds like a vacuum leak)and the engine runs roughly when it is cold (goes away once the engine is warm).  I had a check engine light come on so I attached a code reader and the code 6 has something to do with "secondary airflow?"  Sounds like emmissions stuff to me.  Do you have any idea what part of the emmissions system this would be?

Answer
secondary air is the air that gets injected into a 3 way catalyst in order to perpetuate the burning of gases to bring down Hydrocarbons (HC's).  when that light comes on it means the cats not being as efficient or the air isn't getting to it.  the best thing to do would be to get a better scanner and monitor the O2 readings before and after the cat to determine it's efficiency.  you can also check the hose leading to the cat for airflow.
-cheers