My hampsters urin smells like strong vinegar?

i clean the cage regularly. i have two male hamsters and all of a sudden they started fighting. well it stopped so put them both back in the same cage. well tonight when i came home. the back end of one was torn up and had dry blood on its backside. so i seperated them and while doing so i also noticed that the cage smelled unusually strong. like vinegar. its never smelled like that ever. i have had them for about four months. like its giving me a headache its so strong...is there something wrong? like its really bad. you would think i just cleaned the entire house with amonia. i do not know whats wrong and what to do.