Noise when A/C is turned on

2000 Montero Sport, V-6,

All.

When I turn my A/C on, I hear a clicking noise from what appears to be the compressor. (right side of engine near valve cover - picture below for clarity) It still blows cold air, but could this be a problem? If it is a problem, how much am I looking at in terms of cost for repairing it? Is this a dealer only repair?

I'm a Nissan Guy, I'm just trying to help out a neighbor.

Thanks all...

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Well, I have sene this a lot. If this goes with what i have seen before you just need compressor (when this one goes out of course). I have heard many quotes...$350 and even $600. Havent looked into it much, but i cant see why it would be so expensive as $600. Thats not nessesarily the problem though, but I'm about 90% sure. Ask your mechanic.