Originally Posted by bimmermookie
This is a very helpful thread. I started noticing this squeaking / creaking a couple days after picking up a CPO 2009 328 with sport pkg. Issue was just as others have described. I read these posts then applied Vynelex to both the door seals and the underside of the shadowline trim. It worked completely. I'm expecting it may wear off in a few days, but my local auto parts store didn't have the wax described for the trim, and I was reluctant to experiment too much. Anyway, the fact that the Vynelex worked shows the nature of the problem and points to a more durable solution. Thanks. All!
An update: About two weeks into the experiment, my Vinylex treatment still seemed to have cured the creaking at the door seals. But since I doubted its longevity, and based on the experiences of an earlier poster, I decided to wax the (presumably) offending Shadowline trim. I used Mother's California Gold Pure Carnuba Wax, figuring it was both high quality and less likely than other waxes to be bad for the plastic trim.
A few days since applying it to the Shadowline, a bit of creak has returned, if intermittently. I don't report this to discourage people from trying to wax the tim (there could be several reasons for my experience), but rather to affirm the (at least short term) value of just using Vinylex on both the door seal and the trim. That worked on its own for at least a couple weeks. And I note it is available in disposable wipe form, making it pretty convenient to use and keep on hand...