Engine Noise

I have a 1977 300D with 319,000 miles (50K on the rebuilt engine) that I have owned for about 6 months. I love the car!!
My problem is an engine noise that comes and goes intermittently. At
idle it makes a "chirping" sound like a metallic cricket. Sometimes when I accelerate there is a different noise like a high-pitched metallic scraping that flutters rapidly from loud to soft. At higher speeds, the noise goes away. I've sprayed belt dressing on the fan belts, but that does not seem to help. From the location, I suspect that the source is a failing water pump, but I am not sure, because at idle and with the hood up, there isn't much noise. Also, the noise seems to be more common when the A/C is on.
Is this definitely the water pump, or should I suspect the A/C compressor? What further diagnosis should I perform?
Also, are there any service recommendations if I replace a unit like the pump or compressor, like replacing the belts?
Thanks,
Peter Hollings Atlanta
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One thing it might be is the radiator contacting the fan. The rad can be moved a little as its not fastened rigidly. Try moving it forward a bit and make sure the fastening clips are secure.
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wrote:

On my old 300d the fan contacting the radiator usually indicated the need for new motor mounts.

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Uh, yeah that'll do it too and much more common an occurence.
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Tug on the engine's air cleaner, it may lift due to a broken bracket or mount which could make the noise you describe. Another suspect is the A/C clutch or its bearing. In my experience a water pump will leak before getting noisy. Someone recently posted about needing an alternator bearing so don't overlook that added possibility.
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