The backup singers can be heard talking during the last verse of Mary In The Morning.
These is a 'mechanical sound' right after Lonesome Cowboy has ended. I thought it might be something that happended during a digital transfer, but it is audible on a 1957 pressing too.
At the end of Are You Lonesome Tonight you hear the sound of a plectrum falling into the body of a guitar. I remember to have read somewhere that it was Hank Garland's.
A couple of times, during Teddy Bear, it sounds like Elvis sings "let me vvvvbe... your teddy bear". Once I noticed it... I never managed to 'unhear' it.
I know these are more of these little mistakes, but these are the ones that come to mind first.
Feel free to add. Again: Just for fun!

