Your printer is running Marlin firmware!!! That is a very nice! But it would be good if you can watch the LCD Panel and tell us which version of the firmware it is running.

Usually... garbled characters on the LCD Display are because the ribbon cables going to the display are too close to high current wires for the stepper motors and heaters. Or... (much less often) the 20x4 LCD is a low quality Asian knock off. In either case... if you switch to the latest Marlin firmware, your problem may go away because we have done work to relax the timing for the LCD Displays.