No sound from certain MKV DTS sources

[karbon]

I suddenly have this odd issue with my setup, I'm not sure if it's my blu-ray player or receiver. Not sure if this is in the right category.

Anyways, the issue I have is from certain mkv files I have ripped from various blu-rays and dvd sources.
If the MKV file has dts sound I can't hear it, it will only play DD soundtracks.
I use an external hard drive for these files, and the disk is fine. I've already ran a disk check and it has no errors.

I haven't done anything to the player or receiver. But after this issue I have now reset the receiver and player to factory default, to no avail.

Anyone know what can be wrong here?
I have set the player to output PCM, but I'm thinking that hasn't anything to do with it.

Any tips will be appreciated.

Thanks.