What Is This Small Peak That Always Occurs Within Ketone Infra-Red Analysis?

After looking at a bunch of IR spectrums for ketones, I have noticed this tiny peak that I circled on the diagram below. Does anyone know what it actually is and if I can always use it to distinguish a ketone vs aldehyde?


[![enter image description here](https://i.stack.imgur.com/TbCc3.png)](https://i.stack.imgur.com/TbCc3.png)


