Hm. I don't think it is the audio file encoding as the update time (7hours ago as of this post) matches BEFORE Aiq replied, which means it was already an Mp3 (more than likely). Can you confirm that this was a mp3 before Aiq's suggestion? If it wasnt then there is no need to go further as the preview audio can take up to a day to change.
Also, if you are going to go for ranked status then you need to have the audio bitrate within the 128 - 192 kbps, you'll need to compress it to 192 kpbs
Also, just suggestion but you could try replacing the current audio file with another one that you can find (preferably not from the same source as you got it from since it can lead to the same issue).