Help. 2007 sprinter passenger reg roof van

[sunoG500]

Hi,

I'm looking an used 2007 dodge sprinter passenger van.
It has 14K miles on it. It looks and runs as new except minor blemishes.
The main concern that I have is the big side door. It continuosly rattles when the car is in motion. The current owner told me he took it to the dealership but they couldn't really find out. Is there anyone who knows the solution for this rattling noise?

Thanks