Hello, my name is Rusty. Crackles are caused by digital ICs that are overdriven, or that are malfunctioning. Does it crackle when you play loudly more than when you play softer? This could be a sign of a weak resistor prior to going to the amp circuit.
Remove the screws on the bottom of the piano to open it up. Hold the air about 2 feet away from the circuitry. Hold a vacuum adjacent to the air to catch the dust, and blow it out thoroughly.
Yes, look at the first sentence of the second paragraph. You'll need to remove every screw from the bottom.