Samsung c7 50inch tv

Ive got a samsung c7 plasma and ive hooked it up through a sound system. Im getting some sound delays. Its only on some channels and its only when watching through the tvs internal freeview. It makes it apper that the sound is out of cink. When i play both sound from the tvs own speaker and the sound through the sound system you can hear the slight echo. I am using the same system i had before the new tv but im taking the sound from the tv whereas i use to take it direct from a free standing freeview box. It works fine on dvds and anything else i put into it, could it be the tvs own freeview. any thoughts? :confused: