Vibration suggests wheel out of balance, or could be wheel bearing.
I had a rear bearing fail on my Alfa (related chassis), there was no play, but plenty of noise, the bearing fell apart when we dissasembled it.
Does the noise change when cornering, louder/different in one direction than the other => wheel bearing.
Go for a drive with a friend, get them to sit in different seats, see if they can pinpoint where it's coming from.
If the noise comes from all around, it's tyres.
Do you always drive the same road? I haven't been to the UK for over 10 years, but I remember some of the motorways still having concrete surfaces, which were a lot louder than tarmac.
A Multipla is a big tin box, so it's going to resonate pretty good and make sounds harder to track down than in a car.
Edit:
Jack got there first, I type too slow.