Clicking is fairly normal hamster behavior
While aspen is not toxic,it is still possible to cause allergies which is far more common than most people would think!If you want to be completely certain your hamster will never have allergies related to the substrate you use,you'll have to use something that isn't an allergy causing substance which would mean no wood substrate,no hemp,no hay,etc.Paper based substrates do not cause allergies,but if they are scented or dusty they can affect respiratory health so you must choose wisely when it comes to substrate.