mmm thats very odd. if its only a few seconds it aint the file format / recorded Khz range.
download the latest dirvers for your soundcard.
check in your processes what is running when this happens - i'd imagine you'll be getting spikes of activity.....
can you adjust your soundcards latency value? they often come defaulted to 7-10 ms but youll get better performance out of a cheap soundcard with something in the 20-30ms range - have a play about. As long as your not using it for music creation you can get away with very high latency (90ms) as its just a buffer.
short of than i'm a little lost. the really slow thing has me confused:
the sound file has a fixed playback speed and range, so it can't play back slowly without interferance from software (like pitchshifting [slow down with lowered pitch] or timestretching [a slow down without noticable change in pitch]) both of these effects are VERY unlikely to occur without interferance from software.
now if it's just that the file is taking longer than it should to play through, then it's stuttering, rather than either of the above. that can definitely happen without any interferance from software and is likely to be due to very different issues.
What do you play them with? does this happen with all media players??? cos if it's either of the first two faults, the media player is the first thing i'd replace. try vlc or 'horror' itunes
clarify?