making a seamless loopable continuous audio for games

I got a sound sample, it’s a dentist’s drilling sound. I want this sound to be loopable seamlessly for games. Via game programming, the sound will have 3 parts, the starting part, the middle part and the ending part. When the drilling begins, this sound will be played from the start to the end of the middle part and then loop back to the start of the middle part. When the drilling is stopping, the playing sound will now proceed to play right to the end of the sound.

The thing is I got a non-continuous drilling sound here during those loopings. So what are some of the possible things I can do here to make the sound continuous and seamless?

The start and end points of the loop section need to be as similar as possible. Look for a section where the beginning and end of the section have a similar shaped waveform and a similar amplitude. Then choose “zero crossing points” for the start and end of the section that will be looped.

Note that MP3 files always have a short silence at the beginning, so are usually unsuitable for seamless looping.
Audacity does not support “looping” of samples (it does not support “loop points”) but you can test if a selection will loop smoothly by playing the selection with “Loop Play” (shift+space, or shift+play button).