There is a noise coming from my idler pulley?

I just had the belt replaced in January. I had the mechanic who fixed it look at it and he said it's not loose and that something is probably leaking on it causing it to make a noise. However, I haven't seen anything other than just water under my car which only happens when the A/C is on. And I even smelled the liquid, and it has no smell at all so I'm not sure what could be leaking.