vito 109 2006 rear diff noise ???? help

Hi, please can someone give me some advice,

Parked my van up on christmas eve after travelling 100 miles, van drove perfectly,
went in van today after 5 days and it started great but when i pulled away I noticed a grinding noise at the rear, it sound like something is dragging when the van moves, get it up to 30mph and knock it our of gear and the noise is still there, when you slow down the noise goes just before you stop, can anyone point me in the right direction, just seems odd that the noise has appeared while the van has been stood.

Thanks