The dripleaf "tilts up" sounds play in a loop when you put an item on top of it, wait for it to start tilting, then give it a pulsating redstone signal. It only stops when the item is removed. The tilt blockstate fluctuates between none and unstable constantly. This also happens sometimes when the dripleaf is already being powered and unpowered by a clock, and then you throw an item on top of it.