[Starcrazy]

Hey everyone,
in the last few months I've noticed my 15-year-old cat has started wheezing when she breathes. usually in her sleep. Its almost more of a whistling - in the same way human noses squeek when you have a cold, sometimes!
Anyway, her vet said that he couldnt see much wrong with her, and said it could be cat asthma and if it needed more investigation she would have to be taken in and monitored and xrayed and everything.
The problem is, I've read as much as I can find about feline asthma and this doesnt sound like it. all she has is this high-pitched wheezing through her nose when she is resting or sleeping sometimes. She had a dose of antibiotics from the vet which diddnt make a difference to it at all.
The last week or so, the problem seems to have gotten worse - she wheezes so loud I can hear her clear across the room. but doesnt seem to be in any distress or even wake up when it happens in her sleep.
I know I should get her back to the vets to be on the safe side, but he appeared to have no idea what was wrong with her and she is very set in her ways. she gets extremely distressed travelling and being anywhere strange - I hate to think how stressed and upset she would be having to stay in a vet surgery for days on end. She is old and a little overweight, but in lovely condition otherwise. still I worry I'd make her ill by putting her through tests and observation.
I just wondered if anyone had any idea about what might be wrong with her - or if it could be just a perfectly normal thing like snoring.
I know I should just probably put her through the tests anyway but she is my heart and soul and I'm so worried about doing the wrong thing.
Thanks for your time :)