W204 strange noise between certain speeds??

[The Mentalist]

Hi all, my first post as this is the first Merc I've owned. It's a 2009 Cdi.

When I'm driving between 15 - 35 mph there is a strange droning noise coming from the wheels/tyres? It doesn't happen above 35 mph or when I'm going slowly. I've had a friend check the wheels and he doesn't think it's a bearing?

Any suggestions would be appreciated. Cheers