Our E320 wagon suffers from a REALLY annoying clicking/creaking noise in the rear passenger side door, I'm pretty sure around the latch mechanism.
I have lubed, loosened, tightened and re-tighten just about every single nut, bolt and screw on and around the door area, and drove around without the check strap.
I have spent about half a can of white lithium grease on every moving device and mechanism in and around the door.
I sprayed WD40 under the plastic strip running along the seam on the roof, under the roof rack.
I've had the the inner panel off about 15 times now. Replaced the striker plates. Removed, poked and prodded the latch, forcing some slight re-alignment of various bits inside it with a screw driver.
Nothing. Noise persists, most noticable over small but sudden, sharp road irregularities. It's about to make me completely nuts.
Last resort is a replacement latch which I will try this week. If this is a body flex problem, I will be really depressed.
1995 MB E320 Wagon
2001 BMW 530i
2007 MINI Cooper S (!)