yeah they do that, its a posturing move. Could be in the mood for romance, could be showing the other fish how tough he is. He could also be growing new whiskers. As long as he is eating things are good.
They are HUGE eaters! I keep posting this over and over, but make sure you are properly feeding him. He needs sinking protein pellets (I use large cichlid pellets) and zucchini. I alternate for my plecs. The plecs on my list will destroy a large zucchini between the two tanks in just one night!