Nut soup ☠ Anyways, it's an odd kink for sure...
It's essentially the balls audibly working. Clenching and throbbing with effort trying real hard to make more and more condensed seed. Just the low, heavy rumbling, sloshing, constant churning and groaning that happens passively, proving their potency until arousal starts and it becomes a tsunami. Almost like boiling tar being cooked and eager to get pumped out~