If they smell like rat poo and pee it would be my guess whover you got them from kept them overcrowded. and didn't clean the bedding enough. i bought some when i ran short from a local guy and had the same problem. he must of had 200 rats in each 55 gallon tank. then they end up mounded up on top of each other using the rat below it as the toilet. i actually had to give them a bath with shampoo before i fed them off.