Need some help with sound cutting out

[immortalchaos]

Ok so I have an older Sony reciever. As long as I use DTS or 5.1 sound settings it work fine for the most part. However I have run into a problem watching blurays. I have a problem with the sound cutting in and out. Mainly with music sections, Like the bar scene in Constantine or the end credits of Underworld. The sound just turns on and off. When the sound starts to come back on the reciever says Unlocking on it and I get sound again. It is basically when there is steady sound of some sort. Again like with the scene where Constantine goes to hell. It does it with some movies but not all. Sunshine, the Underworld Trilogy, Etc

Is it just that it is an old reciever? like a year or 2 before bluray came out.