Why does the turbo on my diesel whistle so much?

I recently had my engine and turbo replaced on my Vauxhall Mokka. I am not car savvy and had been on my way to a garage to get the high pitch dentist drill noise checked out. Once I had the car taken to...

Is the turbo on a Mercedes Vito unusually noisy?

I am looking at a Mercedes-Benz Vito 114 but the air intake of the turbo seems rather noisy. The sales guy says this is normal and the van drives well. Is this sucking noise normal?