Smart Doll's may squeak from time to time when posing them which is fine but if they start screeching then it means that they are unhappy about something.
The most probable reason is that some of the grease used in the joints have dried up. If this happens to your Smart Doll then you will need to apply some grease. The type we use is a bearing grease and you can find some on Amazon - or try some vaseline.