Wheezing Random hooting/whimpering at night...

My female who is 2 years old, spayed, blind and 900grams is been waking me up in random nights, that can be days or weeks apart when she suddenly starts making a hooting sound. Of course the first reaction is URI but she has no other symptoms. Even when she's hooting she will still run around and get excited for food, she’s eating/drinking well, no cracking when she breaths, no crusty eyes or runny nose etc. She’s put on 100grams since her ovarian cysts were removed, so although she may look underweight I think she’s doing well.

I don’t think it’s a URI – she seems to be able to stop and start the hooting/whimpering, if it was a URI the amount of times she has done it would have been fatal and she has no other symptoms and it always only happens at night and since my male Hoover was PTS (nothing contagious) – in fact it started the night after.

I looked at the heart page and she doesn’t have any of the other symptoms other than the hooting. Is it likely she would have had x-rays before her spay?

She went to the vets on Tuesday night for a check up and she seemed fine but I did not mention the hooting because she had not done it for about 3 weeks, but then randomly last night it started again.

Any advice?