Extruder clicking

I’m 24 hours into a print, and my extruder has started clicking at each end of the object.

For information, the object is a curved tube, ~ 40 mm diameter, shaped as an S-curve that would be ~300 mm if it were straight, with an external screw thread at one end, and a captive nut at the other.
When running along the mid-section, the extruder is quiet (as normal), but at the thicker, heavier ends, I get the clicking,

I associate the clicking with too much back pressure, as if the nozzle is too low.
The immediate solution has been to increase the nozzle temperature by 5 degrees; this has reduced, but not eliminated, the clicking - we’ll see if the higher temperature adversely affects threads or the captive nut.

Longer term; the clicking is a symptom, so … what should I be looking for to solve the under laying problem?

Other info
Printer: Ender 3 v2
Filament: PLA, branded Ender series.

p.s. I have run several tests of the threaded ends, using grey PLA (same brand), but this is the first run of the whole design, and the first run with the black PLA.
Those prints took ~6 hours, so much quicker than this attempt.