I have a Tech question concerning Audio... Help Please ? :D

[DayShifter]

I have a small digital dj/recording setup.... not the best compared to the past, but it is what it is.....
I normally use Audacity to record dj set's that I do.
The problem I have is this:
Everything is installed correctly (driver's, encoder and software)

• After a few weeks of everything being perfect, Audacity seems to adjust somehow...
  For example, if I do a session at 128 beats per min, the recording comes out slow. If I then take the file and run it through a tempo finder (Tune Explorer) it tells me that the file is 117 beats per min. Substantially slower than the starting tempo

Now, I have thought to myself lets try a different audio recorder.... So I got WavePad (NCH Software).... This seems to suffer the same problem, except from the point of install, as opposed to a few weeks later.
I thought it could be the LAME encoder.... but Audacity uses it for MP3, and WavePad is a wave file recorder.....

Can anyone shed any light on the matter please.....???

I'm pretty insane as it is, and I think this could send me over the edge and into a permanent state of psychosis, followed by a sharp move to the local psych ward.