jack hammer-like noise near power steering pump

Hello, hoping someone can help. I hava a '97 diesel Jetta pre TDI with over 480,000 K (has been running well) I am baffled by a loud noice - sounds like a jack hammer in the vicinity of the power steering pump, but could be referred from somewhere else. The pump does not leak or heat up. Have checked the water pump, alternator, a/c compressor. All pullies are firm. No sign of over heating or leaking. I listened with a rod to the injectors - all 4 running smoothly. The other strange thing is that sometimes there is no noice, then it will start again. I don't understand why the engine is running smoothly - no loss of power. (we are planning a big trip in a week). Alan

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Alan

Alan when is the Noise happening the most when cold or when hot after driving or what?

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http://www.vortexautomotive.com

Hi, thanks for your response.
The noise usually happens after the car has warmed up, and occurs either when idling or driving.
We can hear it from the passenger side. I am wondering about the valve lifters but can hear no abnormal sounds from the valve cover or head.
Alan

Found problem! I went back to thinking the problem was the power steering pump, but on closer examination I found a loose pulley (3 or the 4 bolts were loose) causing it to slam against the hub. Thanks for your help though. Alan

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Alan