Many rats will make URI breathing noises off and on. I have rats that will be perfectly silent and seem healthy, and then one morning a guy will suddenly sound terrible! He will sound as if he has an untreated URI which has been left without antibiotics his entire life! Then next morning? ..... Totally silent again! So weird, yet so typical of rats trying to hide their illnesses. They are masters at deceptive health practices but even THEY can't always hide it and a major flare-up can be too much to hide. This is why I do weekly check-ups to all of my rescues, permanently re-homed rats. I just gently encourage (or force) them to run and be active for a minute so that any hidden breathing issues will be uncovered when I do the rattie megaphone tactic.I endorse what others said: if you're concerned, buy Baytril/enrofloxacin yourself, and put him on it for two weeks. Post back if you need help with dosages. (To me, he looks pretty healthy and I can't hear any breathing sounds in your video.) I understand the rationale for taking your pet to a vet rather than doing it yourself, but so many vets really don't know anything about rats (even the good ones) .