This has been answered on the forums before: Its to stop auto-download robots (downloading code) from downloading the sounds en masse.
But since you and others are bringing this up, I will change it so that the Captcha appears more rarely.
Page Refresh
This has been answered on
Why do I have to constantly refresh the page just to listen to the sounds ?
Strange...as wonderful as it may be,I'm still...up here... floating...and no one even seems to notice.