Hi all
Ao i found that when converting video & audio with handbrake i was getting distorted audio through the ps4.
After some research i have found that this is because of avcodec being used for aac audio, ( i think this is a problem with vlc (?) )
Anyway after changing the audio codec in handbrake to mp3 and adding mp3 in to the Playstation 4 profile in Emby the problem has gone away and the audio no longer sounds like it is under water.
*this isn't a problem with Emby more avcodec i think.
Anyway i wanted to share my findings in the hope that it helps someone else or if i forget in the future.