On my 2.5 98 Boxster the rattle comes from the right A pillar (passenger
side). Somehow the plastic that covers the pillar is a bit loose near the
base, so when the road isn't good is rubs the dashboard plastic. I've
heard of a marine use teflon-based lubricant (MacLube) to use on plastics,
but since the Portuguese distribuitor as run out of stock, I still haven't
tryed it...!
Good luck!

v

98 2.5 986