Just something to keep in mind, since we all heard the noise he's making in his video. Rats are prey animals, which means they will hide any symptoms in a new environment. Unless they're literally at Death's Door, most of them will not show their symptoms in a plain sort of way. They will do everything they can to seem perfectly normal. Some of the common symptoms that we all watch for [for any kind of illness] are excessive porphyrin, poofing of their fur, lethargy, and put off of food and/or water.
My girl Tully came down with several symptoms all at once. She was gurgling, wheezing, crackling, rolling, unbalanced, and very confused. I didn't know what was going on, but I rushed her into a vet, and she was acting perfectly fine. Like absolutely nothing was wrong. The vet thought I was over reacting and told me 'she's not doing it now', and sent me home with nothing but a weak antibiotic.
This isn't to say this is the case with your vet, but something to be mindful of. Hopefully after she hears your video she'll see that he really is congested. If it's in his nasal passage as I mentioned before, she may not be able to actually hear it in his lungs. It hasn't gotten down that far yet.