First steps to take:
Turn off any networking adapters. Increase the buffer sample size. Don't move the mouse at all when tracking if you can help it. Make sure all digital cables are connected and tight-sometimes the pins can get corroded so it's not a bad idea to pull the cable off and push it back on.
Now if none of the above works then you have to go step by step. Start at your interface. Unplug all inputs and record some tracks without connections. Do you still get the crackle? If so then it's in your interface or more likely the computer. Embedded video chips on motherboards are culprits for this type of thing as well as extraneous USB connections and unnecessary mouse movements.
If the interface/computer combo doesn't produce the crackle then connect one piece of gear and try again. Crackle? Swap the cables. Crackle? Continue adding gear until the crackle occurs or you have sussed it all out.