Clean background noise and distortion from mp3 & mp4 recordings

I am looking for a freelancer to help clean background noise and distortion from recordings. These recordings are in both the MP3 and MP4 formats, so I need a freelancer with experience in handling both. The successful applicant should include a detailed project proposal in their application so that I can get a better understanding of their skill sets. My budget for this project is between $100-$500, so the ideal freelancer will keep this range in mind.