My car is making a intermittent whistling sound.

Check for a vacuum leak. I use a small thread and move it around where I hear the noise and see if it gets sucked in between any two mating parts.
Also look for deteriorated hoses.

Thank you for your quick response. It comes and goes? Is that normal with the problem you think it could be? It only started a few days ago and sometimes it doesn't do it at all.

It can still be intermitent.

Here is a link to an explanation of whistling noises in your car and the most likely or first things to check.

Here is the link;

https://www.2carpros.com/articles/car-whistling-noise

I hope this helps you out.