Ever since I had my CM detailed by local auto detailer, I hear a distinct "Creaky" sound at each 4 door windows - Especially reproducible when "flexing" chassis during low speed maneuvers such as one front wheel creeping over speed bump or sharply turning onto raised driveway...When I open the windows even one inch, the creaking ceases

Wondering if there is some type of product which I can apply at window seals to effectively lubricate and reduce the friction of the window edges within their seals -- Certainly, I do not want to apply an oil or silicone product which would be carried onto the window itself resulting in streaking and smudging of the window surface

 

If it's a rubber seal that it's creaking against, the OEM (BMW) product is/was called Gummi Pflege. It is a silicone lubricant, I think, so to avoid residue on the glass you'll want to put on as light a coating as possible at first, then add more if needed until the creaking stops.

http://new.minimania.com/web/Item/NMA7111/InvDetail.cfm

 

I had the same problem and tried everything until finally settled on using WD-40 with a cloth and spreading it on the upper rubber door seal. Not the inner door seal that's attached to the car body but the rubber seal on the top of each door and not the felt part just the naked rubber part.