Prusa I3 extruder, Is there a fix?

[TK Prusa I3]

Hi
New to forum and 3d printing but not so new to Arduino and electronics in general.
I have an issue with my Prusa i3 Extruder clicking/skipping. Have done all the advice on net from clogged nozzle to set voltage for stepper motors..... I even used heat conducting cement between hot mating surfaces( PCU cement to heat sink).
Added heat conducting spacer for grub screw protruding on hot end throat and heat isolating packing between motor and hot-end. Changed motor driver for new, swapped axis motor for extruder motor.
I am at my whits end.
Video of motor clicking and BAD noise when attempting to change filament: https://youtu.be/x3G2vl_UcZc
Video of temparature difference: https://youtu.be/uGUD8P48asM
??? How to deal with the heat creeping up hot end throat?
Whats the noise about when tempting to change filament?
I know (web) heat gun differ to thermo couple... But by that much? (Hand touch suggest that heat gun correct)

I have new motor driver, new hot end and complete extruder on the way (ebay)
Still I do not think it will solve the issue. ANY HELP please.

[William]

1. It sounds like the Z axis does not seem to run smoothly, you can add some lubricant
2. Replace filament may easily be stuck in the throat, leading to "Kaka" noise
3. nozzle temperature is not normal. You should use the M303 calibration PID at first,

If the temperature is still not normal, you may need to consider whether the MOSFET temperature is too high