I'll just repost:

My 98 S70 T5M clutch makes the same sound when the clutch is out (kind
of a fluttery sound, almost like a pump). I can easily hear it in the
garage or in a drive-through restaurant where the sound bounces off the
wall. As far as I can recall it has always done this. I suspect it is
normal.

The most ocmmon problem I have seen reported for the clutch is a squeel
when the clutch is let out. This appears to be related to the
throw-out bearing. Mine has done it for about 30K miles. Annoying but
it has not failed.

I don't recall seeing a lot of complaints about the manual transmission
failing in a major way. The squeeky throw-out bearing, difficulty
shifting (especially when cold) and difficult clutch engaugement from
a stop seem to be the common complaints.