Val,
What a beautiful melody! Nice job. While on your SC page, I listened to a few other songs. You have a nice and easy country style.
I heard the problem you're having with the .mp3 rendition. I'll defer to the real experts but to my tin-ear, it sounds like the .mp3 compression is too high. I heard the same thing on some of your other songs too. Should be a simple fix.
SD