A little while ago I had an irritating little creaking from the bar that retains the shoulder belt to the side of the seat. Spraying in some vinyl cleaner seemed to resolve it but it caused me to do some research on special purpose lubricants that the automotive industry might use for all the various contact points in a car interior that would start making noise over time.
I found this:
http://www.dowcorning.com/content/ne...news_EM30L.asp
And purchased this:
http://www.ebay.com/itm/Grease-Lubri...item3f092ff114
I haven't used it yet, but the cold winter seems to bring out the noise in BMW interiors.