Sound in animatronics is as important to entertainment as the quality of the figure's movements. There is a reason Walt Disney referred to animatronic figures as audio animatronics (he went so far as to patent the name "audio animatronics). Animatronics are not meant to behave like a silient movie. Sound provides an additional dimension of realism to a figure. Animatronics without sound provides about as much illusion of life as a static figure.
With advancements in technology many compaines now offer solid state sound modules that were designed with animatronics in mind. Always avoid sound devices with moving parts such as hard drives or tape systems. Solid state electronics offers the reliability that is needed for shows. The first solid state audio cards, designed for animatronics used solid state EPROM chips. Some lower quality audio cards then moved to using EEPROM chips. Currently, most professional animatronic audio cards use solid state flash memory cards like SD or microSD cards to store and play audio data. Look for some advanced audio cards to add solid state hard drives, in the future.