Mercedes mouse,

Usually squealing comes from outside the engine. Check all the things connected to the fan belts and make sure they turn easily.

Take off the valve cover and see if anything looks broken such as the chain or cam towers.

Turn engine by hand by using a deep socket on the crankshaft pulley bolt and see if you can hear anything unusal.

If chain is not broken, check the cam timing by turning the cam to the timing marks by turning the crankshaft and see if the crankshaft is near the zero mark.


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