There was a neat docu done on Jarrell, apparently quite recently. I found THIS on youtube. I think I hear what you mean, but maybe it just takes some getting used to; it's not as precise as classical which I learned in school, yet it reminds me some of my dad's playing. Not the singing, though. My dad and mom hated what they called "singing through your nose" and we were not allowed to do so. What I hear is overtones and a wavering which is very much a part of that music and I've grown fond of it.

On the other hand, I don't really care to listen to Clements, at all, and I don't think it's because of intonation. I just don't like his style.