Why does my mouse always chew on his cage bars?

Since we got our mouse in May, he's never wanted to chew on the small wooden blocks that we bought for him that were recommended for him at the pet store to satisfy his needs for keeping his teeth in shape. Instead, he ignores the blocks and chews noisily on the bars of his cage. I'm worried because he may be ingesting the paint and metal; also, it's irritatingly loud! What to do?