Crackling that changes with volume points one way. Crackling that is always there points the other.
Narrowing down the cause
A blockage, a software setting and a failed driver all sound different. Identifying which one you have decides whether this is a two-minute fix or a repair.
What to rule out first
Check that no Bluetooth device is connected, that no case is covering the grille, and that volume limits or accessibility audio settings are not active.
Try the free speaker cleaning tool and measure the result before and after.