Engine knock

[Bmies]

Hey guys. I have an 08 Mazda 3I. It's the 2.0 engine. Something very odd happened recently. My oil change date came up. And as I'm on my way to get it done. My car starts to knock. A bottom end knock that's only at 15-45% throttle and any time the RPMS are falling. Anyone have any suggestions or thought on what it might be. If its bad ima prolly be saving for a 2.3 swap