Easy. Pay a bit more and travel nearer the middle.
I have noticed on the -300 that quite low amplitude lateral disturbances, nowhere near worth putting the seatbelt signs on for, are just the right frequency to “pump” oscillations in cups and glasses to the point that the liquid makes a determined bid for freedom. Quite annoying in the middle of the night when you’re not aware of it building up until you get drenched with cold tea...