The loud click/thunk is a good thing - it means that the clock is winding.
Your clock is electro-mechanical; It is a basic clock mechanism with springs, cogs, gears and all the cool things that make a clock work, but it had an electric 'winder' mechanism.
There is a set of points that close as the clock runs. When the points contact each other a solenoid fires and yanks a stationary arm with one of the points down toward the other side of the points on the moving (unwinding) arm. This happens so fast that the moving arm is flung away and winds the clock. As the clock runs the points slowly close until they touch and the clock gets wound again. Over and over and over - until it doesn't.
The main killer of the clocks is low voltage - the points close but there's not enough umph to fire the solenoid so the points stay closed and the solenoid windings burn up. Since they are mounted on a plastic plate the heat warps or melts the plate and the winder assembly is junk.
Another killer is that the points wear out after years of arcing. Normally this makes the clock wind more often, thus burning out the winder.
Occasionally I get a clock that the mechanical portion has worn out - normally the winder shaft has worn it's brass mounting hole into a slot.
I do see a lot of clocks with broken timer springs - always caused by someone trying to 'fix the clock.
The bad news is that these clocks were made by General Time (there's a GT stamped on the back of the case) and they are not as common as the BORG clocks used by Ford for almost 25 years. Parts are not available, you have to make them or salvage them from another movement. Many are pressed together so internal repairs are not worth the time & trouble - even if you can find the parts.
ISI (Instrument Services Inc) is the only place doing the quartz conversion. They have to rework the (overly complicated) set mechanism on the mounting plate to accept a Borg type quartz movement. Last I knew they were charging $155 for the conversion and it has a 2 year warranty.
https://www.clocksandgauges.com/contact-us.html
Personally, I prefer the original thunking, ticking movements. This is odd since all my other stuff is modern guts in OEM cases.