My anecdotal experience:
I've experienced audio issues relating to graphics cards with poor EMI shielding on the soundcard causing it to pick up noise from some gfx card circuit or component. This usually manifests itself as a high-pitched whine audible in headphones or speakers that varies with gfx card load/framerate - this is not the same as coil whine that is audible inside the actual PC case.
If your soundcard is properly designed and manufactured, this shouldn't be an issue.
Also, PCI-E timing issues like on older Creative (yeah, I know) PCI-E cards that used a PCI to PCI-E bridge chip caused things like crackles, horrible latency issues and all sorts of fun symptoms all the way up to BSODs. This can obviously be alleviated by using a decent soundcard with good drivers from a reputable company.
I also doubt these issues are confined to just nVidia or just AMD. The quality of your motherboard and even your PSU can play a part in this too and it's either a lot of research or expensive trial-and-error.