Once we flush our toilet, and the tank begins to refill, it makes a funny whistleing sound. We had the toilet installed about two years ago and never had any problem. There also does not seem to be any issue with the tank filling just the noise.
I am wondering if there is some trapped air somewhere, but don't really know where to begin.
The toilet water inlet valve in the tank is failing, and you just need to replace it. Get a Fluidmaster 400a for only about $5-$6 bucks, follow the easy illustrated directions that come with it, and your problem should be solved.