Have you ever heard a singer that makes you feel a little tense? Maybe there is something that you can't quiet put your finger on… but you know you are just a little on edge while you listen to them? It could be that they aren't singing through their diphthongs properly.
WAIT WHAT??? WHAT ON EARTH IS A DIPHTHONG??? As my private students know, I use weirdo words ALL THE TIME. And, this one, I use more often than many others.
Diphthong – Two different vowel sounds that occur within one syllable.
Watch this video to understand a bit more and see if you might be singing on the “wrong” half of your diphthongs.
PS – I say “wrong” in quotations because some people make a stylistic choice to sing on the second half of their diphthongs. Like in “My Sharona” by the Knack (I know, totally random reference) they sing “My My My I I Woo!” and they definitely sing of the 2nd half of their diphthongs but were going for more of a pop sound, and there are many musicals where that is appropriate.
PSS – If you want to learn more about the magic of Diphthongs – here's the wikipedia link.