Sound problem with some files

Hi,

I have the weirdest problem with some of my files. All of them are mkv and Plex tells me "Audio Profile he-aac".

They play perfectly fine on my computers within Plex. But as soon as I watch them on my AppleTV or my iPad, I get these high pitched distortions. It is not only annoying but makes the files unwatchable.

I tinkered with some settings like Direkt play but nothing worked. I have never had this problem before and I can't tell if it just started recently or has been there for a while.

Any idea what could be the problem and how to fix it?

Thanks.