I have same the problem with almost all movies. Looks like DTS audio problem (my guess), only non DTS movies are OK (tried few - EAC3, AAC, AAC). There is also discussion on samsung forum about that: https://eu.community.samsung.com/t5/tv/smart-tv-ue50nu7400-new-firmware-1320-4/td-p/4000100/page/2
Some people describing same problem.
