Hrm, can you see any excessive wear along the belts? Do you notice long stretch marks, or ding's or cuts in your belt? If not, take the 4 bolts off your valve cover (don't be scared, it won't bite) do you notice if the oils is dirty with (pieces of metal, dirt... ect) in it. If so change to oil. If you notice that your belts are fine, make sure your securing bolts for the water pump are tight, it might be it rattling around. How many miles are on the car, do you drive excessively fast? Could it be your camshaft has finally taken a beating? There are only a few suggestions, if in doubt get a certified person to look at it.
Enjoy
Mr. Porsche