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When my '81 W123 240D is thoroughly warmed up (not when it's first started) it makes an intermittent clicking or chirping noise. It's coming from the area of the alternator and when you squirt water directly on the alternator belt , the noise stops until the belt dries off. I replaced the alternator and still hear the noise. The only other thing on that belt is the water pump which i replaced about a year ago. The belt also looks good. Any theories? Thanks.
 

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Look and see if the bottom of the water pump/crankshaft/alternator pulley is shiny at the bottom like clean metal. If it is the belt is bottoming out due to wear on the pulley itself and that will cause the noise you describe. You will need to replace the offending pulley or you could get a larger section belt.
 

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When my '81 W123 240D is thoroughly warmed up (not when it's first started) it makes an intermittent clicking or chirping noise. It's coming from the area of the alternator and when you squirt water directly on the alternator belt , the noise stops until the belt dries off. I replaced the alternator and still hear the noise. The only other thing on that belt is the water pump which i replaced about a year ago. The belt also looks good. Any theories? Thanks.
I think you answered your own question...squirt water on the belt and noise goes away...got to be the belt.

I had this exact same issue with my '78 308. The clicking sound was actually the belt snapping because it was stretched and loose. Mine also made a squealing (could be described as chirping) sound because the belt was glazed. Belts are sometimes hard to tell if they need replacing. Make sure it is tensioned properly and/or replace the belt.
 
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