Sonos plays some files M4A files using lower sample rate

Hi guys,
I could not find any answer to this problem neither in Sonos's FAQs nor in Sonos forums, so I finally decided to ask myself…

For some reason some of my M4A files, burned via iTunes (not purchased) play with a significantly (slowed down) sample rate. They plan just fine with iTunes, VLC ando there players I tried, but Sonos refuses to parse them correctly.

What may be the problem and is there a way to fix it?

Thanks,
Vic