In short I will say use a rate it "likes" do not try to "buck the system".
Are you using Win10 or Apple Mojave?
Try this. Check help on Export and .wav type. It should describe options. The options say what features the export (binary or function) supports for the given platform.
https://reference.wolfram.com/language/ref/format/WAV.html
I have not checked data rates but I know .wav is a Microsoft format that is a "stolen .au" (Sun audio) and may also have limited playback rates. You may have to check standards on Win10 .wav and assume Mathematica must follow the same limitations. Import/Export functions in Mathematica are not fully documented - the documentation would be too long.