Hide Ubuntu boot errors and show splash screen instead

Question

Whenever I boot Ubuntu, instead of getting the purple splash screen, I get a couple of errors, one of which is:

[drm:intel_pch_fifo_underrun_irq_handler [i915]]

Things I've done:

• Set kernel parameters to quiet splash (using grub-customizer)
• disabled "show menu" and "look for other operating systems" (os-prober?)
• ran: sudo apt install plymouth-theme-ubuntu-logo
• Tried boot-repair on a live CD

I'm 90% sure the issue isn't with grub, but with plymouth, is there any way of just hiding those messages?

The laptop is a Dell inspiron 17R 5720 with both integrated graphics (Core i5 3210M) and dedicated (GeForce GT 630m)

uname -a outputs Linux MattTop 4.4.0-34-generic #53-Ubuntu SMP Wed Jul 27 16:06:39 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux