Good Evening, I have a i420 Kodak Scanner when scanning in images it makes this high pitch screaming noise.

I highly doubt the main board is going bad. There is a huge difference between an electronic high pitched noise vs a scanner noise. Does the noise only occur while scanning or when parts are moving? If yes, then a scanner noise. If the noise is on all the time even when idle, then you have an electronic noise like an open or leaking capacitor.
On this particular model the seperation idle roller builds up with paper dust and will cause a high pitched noise. Like nails on a chalk board. Very simple fix. Open cover. Grab seperation assembly and pull toward the tray at the front of the scanner, it will pop loose then lift up. Make sure to pop it back into place good. Be forcefull. With the assembly in hand, clean, and lube idle roll. It is the first metal/plastic roll the paper touches at the tray entrance. Also clean the shafts and bushings for the rubber rolls. Reassemble and you are all set. Happens on EVERY I420 scanner I have seen.