The feed seems to be OK except that the 'length' attribute inside the 'enclosure' tag is '0' and it should be the file size in bytes.
The episode plays OK in iTunes when you subscribe to the feed. However if you enter the feed URL in a browser there is a double redirect to a ludicrously long URL which does not have an extension (.mp3). This plays in the browser, but when tested in Terminal I got some very odd results (see the bottom of this post, though I doubt it will help much). This suggests that something odd is going on at the server and the Store isn't coping with it. I would advise hosting your files on a basic webspace server, and providing a direct URL to the file without redirects. Soundcloud can work, though it often causes trouble, but I've never seen it produce this result. The URL has 'stream' in it - if you are trying to stream the audio this isn't going to work.
This is the Terminal result:
curl -I -r 200-300 http://cf-media.sndcdn.com/J3ezKarF2vVF.128.mp3?Policy=eyJTdGF0ZW1lbnQiOlt7IlJlc 291cmNlIjoiKjovL2NmLW1lZGlhLnNuZGNkbi5jb20vSjNlekthckYydlZGLjEyOC5tcDMiLCJDb25ka XRpb24iOnsiRGF0ZUxlc3NUaGFuIjp7IkFXUzpFcG9jaFRpbWUiOjE0NjU0MjAwNzh9fX1dfQ__&Sign ature=WQvGeFFoDfqoitr9md~pJ8o6a0ZcbekW4m4aSWSjBJj0zmF1nEdXHoDx3fIjp92OV~HPFd~SkE 2oNd87pjJL4f8EH8gVaPKde1nVbNQpxKD6QtYM8I40utYTBRLYlxlhJd7Kb7e7l3Opjjf2jiXlb11GLz 9sNa6YddR5oIQElhP5nmErZEyuHr7q7Y0TpszKAsPe0lps5n7--2lxObOQgPTcdJ45IlEmWoWY0HUM0y JdsQExHPLIrOzgX6bY~vl6jwcNKrn~jCNNY1rr0**1~odYN0L9qYoOZTPbW2aLnHNowrMJkF3Jj0vAzD -8qTbH9IHpcqVhO8A09sZE3DYcwg__&Key-Pair-Id=APKAJAGZ7VMH2PFPW6UQ
[1] 30597
[2] 30598
-bash: Key-Pair-Id=APKAJAGZ7VMH2PFPW6UQ: command not found
[2]+ Done Signature=WQvGeFFoDfqoitr9md~pJ8o6a0ZcbekW4m4aSWSjBJj0zmF1nEdXHoDx3fIjp92OV~HPF d~SkE2oNd87pjJL4f8EH8gVaPKde1nVbNQpxKD6QtYM8I40utYTBRLYlxlhJd7Kb7e7l3Opjjf2jiXlb 11GLz9sNa6YddR5oIQElhP5nmErZEyuHr7q7Y0TpszKAsPe0lps5n7--2lxObOQgPTcdJ45IlEmWoWY0 HUM0yJdsQExHPLIrOzgX6bY~vl6jwcNKrn~jCNNY1rr0**1~odYN0L9qYoOZTPbW2aLnHNowrMJkF3Jj 0vAzD-8qTbH9IHpcqVhO8A09sZE3DYcwg__
imac14:~ roger$ HTTP/1.1 403 Forbidden
Content-Type: text/plain
Content-Length: 10
Connection: keep-alive
Date: Sat, 02 Apr 2016 04:08:33 GMT
Access-Control-Allow-Origin: *
Access-Control-Allow-Methods: GET
Access-Control-Max-Age: 3000
Last-Modified: Tue, 01 Mar 2016 14:35:59 GMT
ETag: "086d9069069ed62de536cbd4f326d0a9"
Accept-Ranges: bytes
Server: AmazonS3
Age: 86026
X-Cache: Error from cloudfront
Via: 1.1 16291083b92e5aa4f2f272f1da69c5e4.cloudfront.net (CloudFront)
X-Amz-Cf-Id: rRflmD1hPMBOill09dqVTr14kWxybQ4apVJfg9cqNYTN8hm_S_YQnw==