Default [Q] Bottom touch area is erratically clicked - renders phone useless

Hi, a few weeks ago my N4 stated going crazy on and off. but when its on, its ON. i see non stop erratic click traces on the three bottom buttons.
when this happens the phone is unusable since back is constantly clicked. also sometimes the touch seems non-responsive all together.
it comes and goes but and it drives me insane.

I run the latest stock from google.
I wiped the device and the problem immediately reemerged, so I assume it is HW related (Warranty is no more).
I have a replacement digitizer for N4 (only the digirizer part with the chip, not the LCD) and I have a few questions:

1. do you think it is that a digitizer thing?
2. how hard will it be for a very technically capable person with experience in opening and messing with phones but not replacing digitizers to replace the digitizer?