Are you looking for exactly the same sound or sounds like that sound - I will lay odds that it is the later.
If you are looking for an exact match, i.e. the same frequencies at the same volume with the same duration, i.e. if you are trying to find out where a snippet came from, then the pseudo-code is easy:
- Convert both MP3 files to Wave files, (so as to remove the compression).
- Convert both Wave files into a sequence of numbers
- Look for the sequence in the first file within the second file
Since your sample is 3 seconds long I would suggest using multiple files 4 seconds long starting each second of the recording to allow you to pin down the start time.
However if you want sounds like or recognizable things get a lot more complex - as Les Dawson proved over and over you can recognize some music even when you can also tell that every note is just wrong, listen to https://www.youtube.com/watch?v=9nNGlaiVypU.
You need to sample both set of sounds, normalize the volumes, use Fast Fourier Transforms to split things into frequency buckets, decide which duration are near enough and score the similarity.