I was recently putting a new circuit into my breaker box when I noticed one of the breakers was buzzing. I flicked it off and back on and it stopped. It then started buzzing again. I thought bad breaker so I replaced it. Same problem. I then went around the house to trace what was on that breaker and found that a motion sensor switch in our pantry caused the problem. When the light came on the buzzing would start. That is why when I flipped the breaker it turned off the motion switch and didn't buzz again until someone used the pantry.

What would be causing this?

Thanks
Gary