Merc Sprinter Problem?

Have an '08 311 cdi, pre heat warning light stays on for approx 2 mins then goes out, seems to be a vibration around 40-50mph, had the front wheels balanced 2day but no difference also an audible 'clicking' when i press the accelarator....noticed a small pipe near the air filter unattached, was running great until a few days ago when i had it in the Merc dealer for a fuel leak..all probs related or just falling to bits!!!?