This sound getting a bit louder, only when A/C is running but it’s not constant when A/C is on, just a lot of the time. If I turn off A/C, it stops immediately. I’m on third floor of my apartment complex. What could it be and does it require repair or can

This sound getting a bit louder, only when A/C is running but it’s not constant when A/C is on, just a lot of the time. If I turn off A/C, it stops immediately. I’m on third floor of my apartment complex. What could it be and does it require repair or can