can't say i have the 'creak' in my car. you are referring to the B-pillar area i figure. i presume it is one of the trim pieces rubbing against one of the others. you could try dismantling that area, ensuring it's all secure, and refitting everything. but removing the rear side trim takes a lot of work, including removal of rear seats to access all the screws/clips.
or perhaps it's a door/window seal? give them a wipe/spray with some silicone spray if they appear dry and aging.
a change in suspension compliance suggests something is worn. quite likely one of the bushes, like a front top wishbone, or lower wishbone. how many km's has your car done? they are a 'consumable' item, so need replacing when worn, which can occur after about 80K+ km, depending on road conditions.