A few weeks ago, my radiator had a severe, but easily patched radiator leak. I think once it got a little hot (though the by the temp gauge it was still ok). In between the time the leak was present and the time I fixed it, we noticed a clicking sound constantly. I remember hearing the click while idling cold, but it would not sound while driving. I found that the source of the click is some sort of auxiliary object off the crankshaft that clicks when it engages. I have posted a picture here: http://www.et.byu.edu/~jaa39/volvpart.jpg Sadly, my haynes manual only shows the 760 diagrams and photos for this area, and I can't figure out what it is. In the 740, it is directly below the alternator. The belt is always spinning on it, but you don't see the faceplate move unless it clicks. It would engage for a few seconds, then click off. It would do this every 10 seconds, roughly. After driving on the highway at about 45 mph for about an hour, it no longer activates at all... even while idling. The car seems to function normally without it, and it even runs cool. What is this? Do I need to get it repaired?

Thanks, Alan