[souffle]

I'm in the UK so don't use aspen but we do use Megazorb which is similar to the Carefresh. In our experience certain colours do have a more pungent odour. Cinnamons are the worst and cinnamon based colours I have noticed. Maybe you are quite sensitive to the smell? Overcleaning can make them mark more so I would monitor this and see if the smell is only there when in heat and if it is the actual hamster who smells or the substrate because really it should only be her who gives of a smell.