A common installation error we see that results in these symptoms is when the speakers are mounted in the vehicle and the mounting holes are drilled with the speakers in place. When the drill bit is withdrawn from the hole the material that has been removed (metal or wood etc ) can drop into the speaker and/or voice coil resulting in speaker failure. This is not covered under the product warranty. Always use the provided template to pre drill the mounting holes.
Another cause of distortion or crackling is a burnt voice coil which is a symptom of overdriving the speakers or delivering a clipped or distorted signal to the speakers from the source unit or amplifier. You may be able to smell the coil is burnt or by gently applying even pressure depress the cone of the speaker and you will feel if the coil is rubbing or binding.
Mounting speakers on an uneven surface can also twist the frame out of shape and cause the voice coil to rub and cause permanent damage.
Insecure wiring or poor connections are common causes of crackly or distorted sound from speakers. Check all wiring.