I'm pretty sure that is from too much pressure on your eardrums, when you're levelling in heights, Kellan.
Too much earwax is making the clicking noise and increases the pressure (you'll hear/feel that also when you swallow), the 'plop' is your eardrums getting in their original position again.
My advice, if the plopping gets annoying or painful:
3 days, before you go to bed, a few drops of arachid oil in your ears and use some cotton to prevent from leaking. Then visit the doctor and let him clean out your ears.
NOTE: usually if you decide to do that, you'll probably have to go back once a year to repeat the treatment. Therefor: no cottontips ín the ear, cottontips too deep in your ears can trigger the production of earwax and you'll only push the wax towards your eardrums, instead of removing it.
And use earplugs whenever you're going to be in loud sounds.
The delicate sounds of thunder are devastating for the ears, if one wears no protection!!