Between 600 and 650 rpm, there is a grating sound at what appears to be around the water pump. No leakage is evident around the pump. 700 and up, noise goes away. Coincidentally, I had the serpentine belt replaced a few months ago and the noise became evident after the replacement.
Is this the beginning of a water pump failure?

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Walter Sawczak
1990 300 E
1993 Lincoln Mark VIII
1983 Jaguar XJ6