Toyota engine clicking when AC is on

I own a Toyota Avensis 2004 1.6 petrol, whenever I turn AC on and I drive a high gear with low rpm or even low gear with low rpm it makes a clicking noise as shown in the video below, what could be the cause of this or what should I try to identify the problem?

https://www.youtube.com/watch?v=2C9aqV_-NmE