What is causing cracking and creaking noises in the ceiling and walls?
You're saying that noise occurs when the AC is running. Is it possible that your AC's refrigerant line runs through or above your bedroom ceiling? If improperly installed, it may rub against structure when the line expands/contracts as its temperature changes, creating the noise.

It's also possible that a noise could come from air ducts in your ceiling/walls, but from your description the most likely culprit is thermal expansion/contraction of a metal pipe/tube rubbing against wood.