[T16]

From the BMW forums:-

Originally Posted by BMW Forums

In my experience, it is the simple and effective solution to the window/door noise that most (early?) X3 owners seemed to encounter.
There may be more than one type of noise, but this is the one that is silenced by lowering the window, even by a fraction from its fully closed position.
Early on, many dealers were apparently trying all sorts of solutions, such as realigning the door, often making matters worse.
BMW even had a new, replacement door seal, covered in a bulletin, which also failed to be the full solution - maybe because of installation shortcomings.
I did not have the problem at all until suddenly during year 3. The dealer used Gummi-Pflege (or an equivalent, SA wasn't able to tell me) and it is still fine after nearly 2 years.
He advised me to think of it as a maintenance item.