What causes some bootleg sounds to distort?

Who's got the knowledge of why some bootlegs may crackle or distort on some sound effects at times and maybe not at others? Does this have anything to do with the type of motherboard you play them on or is it a defective cart? Anyone know?

shitty soldering

shitty soldering and poor circuitry are the main culprits.

My guess that other things could also play into effect.

Poor componets (sound ships that degrade faster), Incorect copying of original sounds, squeezing or resampling of sounds (don't know if this applies to neo tho). Or maybe poorly desigined setups are over/under blowing the sound circuitry.

Has anyone ever experienced this? I know someone who has a bootleg MOTW and the sound works flawlessly on his one slot, but not on his muti slot motherboards. I find that a little odd.