I was talking to the service manager down at the factory last week when I dropped my car off for its first service about BB noise and they have found that most of the noise is due to the metal to metal mounting of the BB. There is no anti vibration mounts or cushioning so you get a resonant harmonic vibration through the chassis which amplifies the noise. So they mounted a known noisy box into a car with some rubber cushioning and it was quiet. If its a problem to some owners perhaps putting some high density rubber under the mounting flanges might be the answer.
