Rhytmic noise at ralenti

I bought my Sharan tdi 115 hp last january and when working at ralenti ( +- 900 rpm ) i heard a rhytmic resonance coming from the right side of the engine. When i turn the steering the noise increases. The ralenti is always OK. The dealer changes the timing belt but the noise remains equal. As you know the Sharan is assembled near me at Palmela - Lisbon, and two VW engineers heard the noise and they say it's normal, although other Sharan's don't make any noise.

Could somebody help me with this ?

Thank You.