Laptop makes speed of audio recordings fluctuate

I was recording a duet for a song I had recently arranged for piano, and everything went well until I tried to sync the two parts I had recorded. When I put it into a video editing software, one of the two parts would sometimes be ahead of the other one, and sometimes behind. I checked the two parts against a metronome, and realized that although I had initially recorded the two parts with a metronome, the audio recorded by my laptop would slow down and speed up at random intervals. To further test this, I recorded a metronome ticking at 100 bpm, and played the recording on my laptop with the same metronome ticking the same bpm beside it. Turns out that my laptop skews the speed of recorded audio! Although it doesn't mess up the speed too much, a difference of half a millisecond between two duet parts makes my song sound like a drunk man banging on a piano. Have all my hours of work gone to waste, or do I still have hope?

It's possible the laptop had lagged when recording and recorded the notes at slightly incorrect intervals as it was thinking more at certain points than others. This is potentially fixable in the software (was the audio recorded to a MIDI file? or just an audio codec like mp3). It's also possible that the video editor is playing back in a lagged manner.

My laptop seems to record wrong every time, though. As I mentioned, I did several tests, and the audio came out wonky every time. Could it be possible that it is because it was a video (mp4) file?

StupidDogEater

Suggestion: Look at Kari's My System Specs and fill in yours, might help provide more insight to the problem. Also check his solution for cooling of a Notebook/Laptop, any additional cooling can cause better stabilization.

I've had a used laptop that would do that, just the slowing down part. Made me give up a lot of work writing a program to record pen strokes. If all fails, get an external USB sound card see if it helps.