As suggested in the article “Why are my speakers producing an excessive noise?” Crackling may suggest there is a loose connection or some interference within the system.
Bad quality/cheap cables can sometimes be the simplest cause of this noise, by changing them out for a newer or different set this may remove the sound. Also ensure all connection points are clean, over time certain types of cable may start to oxidise causing a dull sound and possible some interference. If the cable is a few years old try cutting it down slightly to reveal some fresh cable to make the connection with.
If this does not resolve your issue, please also investigate the following articles:
If none of the above or alternative articles has resolved the issues you are experiencing the last point of reference will be within your speakers. If your speakers are under warranty at this point, we would recommend reaching out to your place of sale to organise a warranty inspection/repair of the speakers.
If your speakers are no longer within warranty, please feel free to submit a support ticket for further assistance.