Mine is a diesel. I can say sound level is equal or more than polo. When you are inside cabin it would be silent but once you cross 100 kmph slight sound wil be audible as in all diesel engines.
If only VW started showing their German-ness or whatever and gave us some decent sound deadening or something. Compared to the Polo and Vento, Hyundai and Maruti diesel cars sound like a petrol-engined car on the inside.