Dolphingirl: Here is some info about the 5 S's:
http://www.thefussybabysite.com/coping/the-happiest-baby-on-the-block. I would also HIGHLY recommend getting the book and/or DVD! It's great that you're swaddling him and using white noise, but sometimes it just takes the right combination of soothing techniques to get them sleeping right.
The unpredictability is most definitely a key trait of high need babies! (and, in my opinion, one of the most annoying traits!). My son has always been unpredictable, in pretty much every regard. He's much more predictable now, as a preschooler, though. In fact, he works very well with routines, and actually really seems to need them.
What worked for Sammy for naps was to swaddle him (very snug!), put on the white noise, and jiggle him up on my shoulder. This almost always knocked him out within a minute!