Not sure, it's fitted to the rear of the roof, short black ariel. How do a get to the ariel earthing OTOMAN
The earth problem is at the radio side, You need to pull out the radio and check all the connctions etc.
Try not to disconnect it if you don't have the code for resetting the radio.
Click on the link below for some info or use the Forums search facilty input - Scenic reception and it should throw up some info for you.
Renault Scenic - Poor Radio Performance*fixed*