My pi 4 isn't overclocked - what settings would you suggest I use for that please?
I don't have any recommendation, as i said i don't own a pi4. I'm just thinking that garbled sound can be the result of performance issues, and gpgx appears to be surprisingly demanding. So i'm wondering if an overclock could improve things.
should they be enabled?
Probably not, they are features that will lessen performances.
On a sidenote, savestates with the nuked setting appear to be broken to me : i just tried loading my savestates from yesterday and the core crashed, after some more tests it appears the core can't load savestates from another session on my setup (it works just fine if i set it to MAME). That might be related to your issue. Maybe report this to the author, and/or change setting/emulator.
There are no performance issues whatsoever playing a game with nuked sound in the initial session
Your sidenote issue IS the issue that I have been concerned with the whole time. Thank you for corroborating that. I think this emulator is the only one with nuked fm sound.