My past boys started like this and it got increasingly worse. Antibiotics and antiinflammatories didnt make a difference. Vet said chest felt firm and not springy so indicative of lung tumors. They both progressed to the point of having to put them both to sleep on seperate occassions. It was very sad. I hope its nothing to worry about but without a video we cant really tell you. It might be brought on when excited and playing as this is causing more of a demand on the cardio respiratory systems. When relaxed they dont need to breathe so hard. Do you see any other symptoms?