I seemed to suddenly have a 3D issue on my otherwise trusty Raspberry Pi2, so I ran the January update on it, which resulted in the audio from any video source now being output as nasty high pitched digital noise in stereo … 3D works again though, haha …
Any ideas, or anyone else getting this?
It sounds like you have passthrough enabled for a format that your receiver does not support. This can be adjusted under Settings -> Audio.
I see your point, this being a Rpi2, but firstly my receiver supports everything, except IMAX Enhanced, including Atmos, and secondly, in this case even straight DTS 5.1 or AC3 Dolby 5.1 stopped working 
Some logs may give some clues here
I’ll look into that as soon as possible. Thank you so far!