How to get media link in sitecore rss feed

I am setting a feed for media items in sitecore and followed the setup guide and everything works ok. However, the link tag in the feed generates the absolute path to the media item in the content tree, something like this

What we want is the url to the image on the server like http://ecms-site1.intlsos.com/-/media/corporate/..../incident-occurs.mp3

I inherited from PublicFeed class to add extra property in the rss feed, but need help changing the behaviour of the link property to return the media url.

thanks