Hi, excessive shrinkage is over 2mm on ceilings and walls & 4mm on stairs , so your builder should address this .
Creaking floors can be a number of issues ,most common is the metal stud walls ,sometimes this can be fixed in 10mins with a small wedge other times it can be more involved . It really depends on a number of factors , the type of noise , the construction and the experience of the contractor carry out the remedial works .
Regards Maxell