Have a look at this image:

http://www.valisys.com/people/krn/dash.jpg

that is my 98 S70. The circled point shows a rough edge.
That was the leading edge of a piece of plastic (it was straight)
that would rub my glass and squeek. I mangled it with some tweezers
to stop the squeek. Sight down your A pillers to see if you can
see this. In the photo you also see the plastics reflection in the
glass. You can also see it from outside the car looking down into
this area.

I slipped a business card down there to initially fix it then mangled it
while trying to pull it out (which worked to stop the squeek).

As I recall, I only heard it then it was cold. I guess when it was hot
something expanded and the plastic would no longer just be barely
touching the glass.

I've posted this a couple times and so far nobody else
had this as a source of a squeek. So, its a long shot.