I´ve bought 2001 S60 2,4T couple weeks ago

now when the weather became cold my car started to rattle some part of my interior while in low RPMs - its something in the back and the noise sounds like some plastic part would vibrate on another plastic.
after i cross some level (1200-1500) of RPMs the rattle stops - so its RPM based Rattle.

anyone experienced this? any ideas what to look for and what do do to cease the rattle?
ThX

 

Does it sound like it's coming from the C pillar trim? I heard a similar sound at start up when the outside temp was below freezing. Once the interior warmed up, it went away.

 

it kind of does - its probabaly the C pillar - it started with winter, ill see if the problem continues in the next summer - now i dont see much to do about it. maybe its just the cold weather