When looking for audio to include in a multimedia project, it is important to be aware of how format and sample rate can impact the quality of your audio. Mp3 files compress sound files while .wav files are uncompressed and can store higher quality audio.
The standard sample for a project that combines video, image and audio elements is 48kHz. It is important that you make sure all of the files you download and record are the sample sample rate. You can check your files resolution by opening in a media player or video application and checking the properties of the audio file.