Can't see GRUB menu on Boot, Chromebook

I've installed Arch 2017.07.01 on a micro SD card in my Dell Chromebook 13 using [this guide](http://lifehacker.com/5680453/build-a-killer-customized-arch-linux-installation-and-learn-all-about-linux-in-the-process) , and I'm using [John Lewis' SeaBios](https://johnlewis.ie/custom-chromebook-firmware/rom-download/) to dual boot. I can successfully get into the boot menuand select the micro sd to boot from, but I then get a Welcome to GRUB! message, and, instead of a GRUB console, i get a few lines of white distortion on top of my screen, with the boot menu still frozen in the background. I believe the distortion is the console outputting incorrectly as typing seems to change it, and it disappears after a while, reappearing when i move the mouse or type, like the screen falling asleep and waking up. I've already tried doing a full reinstall of arch, commenting out GRUB_HIDDEN_TIMEOUT and GRUB_HIDDEN_TIMEOUT_QUIET, and changing GRUB_GFXMODE to 640x480, but nothing had worked. Any ideas?