can you add this to the PKGBUILD in the grub prepare section

    #### Remove grub messages
    if grep -q "Welcome to GRUB!" "${srcdir}/grub-${_pkgver}/grub-core/kern/main.c" ; then
    sed -i 's/Welcome to GRUB!\\n\\n//g' "${srcdir}/grub-${_pkgver}/grub-core/kern/main.c"
    sed -i 's/loading//g' "${srcdir}/grub-${_pkgver}/grub-core/boot/i386/pc/diskboot.S"
    sed -i 's/.asciz "GRUB "/.asciz ""/g' "${srcdir}/grub-${_pkgver}/grub-core/boot/i386/pc/boot.S"
    sed -i 's/.asciz "."/.asciz ""/g' "${srcdir}/grub-${_pkgver}/grub-core/boot/i386/pc/diskboot.S"
    sed -i 's/.asciz "\\r\\n"/.asciz ""/g' "${srcdir}/grub-${_pkgver}/grub-core/boot/i386/pc/diskboot.S"
    fi

theres no need for those messages if grub isnt going to load then you will get a black screen or default to shell printing a welcome message serves no purpose