The power supplies that come with these USB converters are mostly of very low quality and often fail but shouldn’t make the hard drive tick, perhaps the hard drive is not very good and you only notice it ticking because it is outside of the case.
The main thing that you should check with USB to IDE converters is the reliability of reading the data from the hard disk as many of these devices have an error rate of about one error in every 3-4 Gig transferred. Check out the web page below for more details on this.
http://bigacid.wordpress.com/2008/12/08/jm20337-read-data-corruption-solution/