Nothing to do with being fixed.
He is doing it A: Because he can and B: Because when he has done so in the past he has gotten something out of it.
He whines, you open the door to let him out. He knows that whining works in that situation and is smart enough to make an attempt to see if it will work for other things.
You can't ignore him but still try and figure out what it is he wants!
Either ignore 100% until he stops which will be harder for you or realize that he is well on his way to training you.
My girl started whining when she was about 3. She has perfected it and pretty much gets whatever she wants. If the whine doesn't work fast enough she will sit and stare WHILE whining and then touch me with her paw. If those combined don't work she will add in a little huffing and puffing, a snort or two and a face that is hard to resist.
I'm a sucker who has been trained. The first step to realizing that you have a problem is to admit it. :D