Jamillionaire

I have been have a noise issue in my car. There is a high pitch noise that completely goes away when the climate control is turned on but comes back on when it is turned off. When the climate control is off the noise also changes with the rpm for example at 1500 the noise goes away but under 1000 it comes back on. I thought it had to do with my stereo but I have tested everything related to that and ruled out that it was causing the noise. I read on here people having the same issue and it was a vacuum leak for them, how would I find out if there is a leak and does it sound like that is the issue?