Well, today was our first day of the year where temps got up to the 80s, and today was the first day in a year where the headliner in my G70 started making the annoying crackling sound, right on cue.
It's completely temp related, either due to thermal expansion of some component, or due to softening of an adhesive. The sunroof being open or closed makes NO difference, and the noise only comes from the passenger side, right around the top of the A pillar and the passenger grab handle. (Sorry, I know for most of us this is old news.) That's interesting, since there's no grab handle on the driver's side, and no noise. May be related.
I also found that pushing hard, sideways, on the headliner on the driver's side can cause the noise on the passenger side, like the side force is pulling the headliner shell away from the roof/body on the opposite side. Which again makes me wonder if the aggressive is giving way, maybe due to complications around the mounting of the passenger grab handle.