Grinding noise from Engine compartment
 

Car: 1993 500SEL

A grinding noise is coming from the front of the engine - "by the belt".

As best as I can determine - it's coming from a device on the belt, on top of the alternator. The black plastic on the left of it vibrates simular to the grinding noise.

Is this an air pump?

Thanks for your continued help.

Comment: I just had the water pump replaced - what is it now?

Well, if the noise is coming from the front of the engine and you determined it is coming from a "device on the belt", next step is to determine which device. With the engine running, using a mechanics stethascope, long screw driver or wooden dowel rod, you can listen to each of the accesories individually. Use extra care as it is easy to accidently get wrapped up in the drive belt(s). When you reach the offending accessory you will hear a definite difference in the internal sound - most likely a bearing heading south.

See if the dipstick support is rubbing against the water pump pulley.