Can you tune it out by bumping your extrusion multiplier? I've run 3 kg spools more or less exclusively for like 5 years now. They ride on ball bearings though. I do print the occasional 1 kg spool and don't have issues swapping back and forth.

Perhaps you can grease it up, or use (print) a mount with ball bearings. Or you have to stand there and feed it until the spool is done

You might try greasing the dowel.

Bugger. Have you got a workaround? Or are you now an automated feeder for the next 2kg?

You mentioned already having smaller spools, can just transfer some of it there. Best of both worlds, if a little tedious

Ig you think that's bad wait until you get multiple retractions going that the rocking motion of the 3kg Is probably going to be enough to pull the filament right out of the extruder.

I have my 3kg spools above the printer as well, not having your issue, I think the difference is I'm using a guide pulley on a skate bearing to direct the filament straight into the extruder.

Others have suggested greasing the dowel or using bearings, and if the issue was friction, then they'd be right.

If the issue is inertia, then this won't help. Accelerating a given mass to a given velocity requires a certain amount of energy, no matter what.

What could help is something similar to a Huygen drive, where the filament is looped around a large wheel (large enough that the filament can curve around it without breaking) which is able to move against a spring or counterweight. This would allow the movement of the spool to be "averaged out" rather than accelerating and decelerating sharply on every extrusion and retraction.