How in the world can I get my hamster to stop biting its cage bars?

I have put a sock on where he usually bites and he has been biting the sock for a few days. Now he's just changed locations. How do I get him to stop? I have heard of coating it with something he hates but what & how? He's not looking for attention because I have take him out for periods of time and put him back in when he seems bored and just bites. I have 2 empty chew sticks ( just the wood left now) & a chew stick with seeds ect. I also have toiletpaper tubes, a salt lick which he NEVER uses and a willow ball. It is bad to leave him alone? Because I don't mind but i'm pretty sure its bad for its health.