I adopted a 4 year old male (neutered) cat about two weeks ago. I've taken him to my vet and he is physically healthy. He is very affectionate but has bitten me twice (breaking the skin) since I've had him.
He becomes very agitated when I leave the house or come home--hissing and growling. He seems to want attention, but becomes hyperexcited even when I pet him.
The first bite was as I was coming home from work. The second was on my bed as I was petting him and he was outwardly calm. He has tried to bite on other occasions as I've left the house or come home. I've taken to isolating him in a spare bedroom before I leave and then letting him out when I go to bed, but I know this isn't a long term solution.
You may ultimately have to discuss this with your veterinarian and discuss anxiety medication for him. I'm not at all certain this is separation anxiety. It probably isn't.
I strongly suggest you read this page very carefully. The procedure outlined there is very likely to solve the problem. And, irregardless of other tools used and ways you work to modify this behavior, I strongly recommend using cat pheromone products to help create a more calming and safe atmosphere for your cat and make the work you are doing to change his behavior more likely to "stick."