Why is my cat so freaked out and skittish?

For the past month or so I have noticed that my cat has gotten a new personality and now freaks out and becoming very skittish and I cannot figure out what could've happened to cause my cat to act weird like this. Every time my dad raises his voice or anyone coughs or he hears loud sounds my cat freaks out and Mom can't even hold him to settle down because my cat gets very skittish and tries to scratch but not attack and Mom has gotten scratched twice by him. We first thought my cat was showing signs of an earache that might be the cause of this strange behavior and the loud noises were damaging his ears but we found nothing when we looked in his ears. The only thing my cat does have are sinus troubles but I don't think that would make him do this weird behavior. My cat has never had this problem and has not been abused in any way and could my cat be ill?