OP like I said it's the same noise mine makes, random and not constant. It does it all the time (randomly) when the climate control is on, and much much less when it is off (never really).
Unless it is bugging you that much I wouldn't worry about it. Mine has done it since I bought it 4 years ago at 49,000 miles, and hasn't got better or worse in 4 years and another 65,000 miles (112,000 on the clock now). Air con still blows super cold and works perfectly.