I accidentally left my 10ms-interval "f"-spam makro on an apple tree running for a few minutes, and produced hundreds or thousands of items.
Luckily, the engine is smart enough to not render items that share the exact same location in the world. However, the inventory screen is not.
So every time I went in the inventory menu with the apples on the ground displaing I got ~1fps and constantly zombie noises.
No zombie noises get played when you don't do anything. The zombie sounds only play when you make sounds (walking, brushing against the tree, etc.)