Hmm sounds like when I first got NAV.
If you're not savvy under the bonnet then leave it closed and go to a reputable mini workshop like brikworx and get them to sort it out as it can be a number of things.
As far as the noise goes it's pretty normal for the rear of the van to rumble a bit as it's a big empty drum (tap the roof and see)
Firstly check the seals on the back doors so you don't get fumes in the cabin.
Second put some carpet down in the load area as it will noticeably quieten the rear.
Thirdly if the car has been sitting around for a bit the tyres have probably got a flat spot which sounds like a dud bearing, also while looking at your tyres check them for nicks, cracks and other damage.
With the tyre pressure I used to run 32psi front and 28psi rear for comfort and 38/34 for my trips into the hills. This combo had the best feeling for me.
Oh and most importantly enjoy mini ownership!
Ahh memories of a newly aquired Van

I forgot how bad NAV was when we rescued him. anyways much blood, sweat, tears and swear words later.
