it sounds like your cat may just be getting bored being alone. a lot of times destructive behavior can be traced back to an animal being bored. its like with kids; "there wasnt anything better to do". if you can stomach the electric bill you might try leaving the television or a radio on while youre out. something for the cat to hear people talking and make him think hes not alone in the apartment. other than that you may need to put him up in a crate or bathroom while youre out to minimize the mess