I just come back from the garage taking a closer look at the engine belt. This is the simptom:
Start the engine from cold, air pump is making a noise like a drum.If I am covering the air intake from the pump with a finger I feel the vacum suction, and the noise goes away.By taking off the finger from the air pump intake the noise comes back.
After engine warms up I am starting the a/c and no noise yet. But I have asked a friend of mine to sit in the car with the foot on the brake and the shifter in D position.
Now, whenever the cicle of the a/c compresor begins(after the a/c clutch engages) i can get a noise coming from the air pump like a rumble. I was trying to locate the noise but I was not able to do it.
What it puzzles me is, if the engine is warm, why the pump is making noise. Or could be something else.
Please help me with the diagnostic.

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New Addition to the family
2013 Passat TDI 5Miles
2004 E500 4MATIC Wagon 95k
1996 E300 Diesel 173k Sold
1993 300E 2.8 230k Sold
1994 E320 White Wagon 373K Sold
Still dreaming about ....500E


Radu Negru