Any audio recording will have its own copyright separate from the base text, so it'll be a while before any quality audiobooks enter the public domain.

For now, your best approach would be to take high-quality ebooks like what Standard Ebooks offers, and use text-to-speech software.

Librivox creates audiobooks of PD texts. I've heard good things about their work but I personally don't listen to any audiobooks in general.

There's a compelling listen: https://librivox.org/the-first-fifty-digits-of-pi/