xset doesn't work in Xsetup_0

[Rob Whitlock]

At xenodm's login screen pressing the Fn key makes a beep. I put the lines

${exec_prefix}/bin/xset b off > /xset.stdout 2> /xset.stderr
echo "Error code: $?" > xset.ret

at the end of /etc/X11/xenodm/Xsetup_0 yet the Fn key still makes a beep.
There is no output from either stdin or stdout and it returns 0. How can I
disable the beep? xset works correctly in ~/.xsession.

Thanks

Robert