Pops and crackles can usually be fixed by adjusting the buffer length on your audio driver. If you are using FL Studio ASIO then you can adjust this by going to Options > Audio settings > Click on Buffer Length, select a higher buffer length, usually 512 or 1024 is enough but you may need to go higher. Keep in mind higher buffer lengths can increase latency, making MIDI keyboards and other instruments difficult to play and record live.