So funny thing, I was working on North By Northwest last night and I found a section were the Blu-ray's 5.1 is missing some sound effects. When Cary Grant is escaping from the hospital outside on the balcony the 5.1 is missing some sounds of his feet and struggling moving balcony to balcony. It occurs around 1 hour 54 minutes
But it is present on both the Criterion and MGM laserdiscs. Nothing exciting and it is only a few seconds but interesting nonetheless.