Well, with the rolling and "click, click, click" I'd settle on the bushings and a possibly damaged/broken parking pawl.
Be sure to keep the hand brake adjusted and use it religiously. As TexBill experienced, I too, woke up one fine morning to fine my Benz in the middle of the street. Good thing I live on a quiet road with little to no traffic at night.
The bushing are cheap, getting time to replace them is the toughie.
73 280 SEL 4.5