Why is my hamster sneezing / coughing?

My 8 week old panda bear hamster (Bandit) makes these "puffy sneezing/coughing" sounds. He displays no other symptoms of illness (Well groomed, eyes wide open, ears raised high, no eye/nose discharge, dry poop + clean bum, active, eats lots of food and drinks plenty of water). I read that it was possibly the bedding and did some research on the brand that I was initially using (Carefresh Odor Control) and found out it's a super dusty brand. I'm baby sitting my girlfriend's hamster who recently changed over to this brand and noticed that he (Oreo) started sneezing too as opposed to before. So today, I bought them both new aspen bedding, and I cleaned all the dust out of everything thoroughly. Why are they both still sneezing? Are they just in the midst of expelling remaining dust out of their system or...? Bandit has access to plenty of hamster pellets, a dish wheel, mineral stone, salt lick, and water. Same thing for Oreo except no salt lick and has a wheel as well as the dish wheel. Both hamsters are using the "Sunthing Special" aspen bedding brand. Please tell me if I should bring them in to my local pet store (That does free diagnostics within the first 5 days of notice). Thank you!