Porsche Cayenne help.

[Lancerevo]

I have a Porsche Cayenne which I bought a few weeks ago, 3.2s auto 2006 75,000 miles. And while I am driving at about 30 I can hear what I can only describe as a loud dull drone. Not a knock as its constant over 30 and does not go away until I go below 30 again. It sounds like it maybe a wheel bearing but the sound seems to be coming from the front/middle of the car.

There are no knocks or bags to go with the problem.

The car has 20 inch tyres on genuine wheels.

The noise It's driving me nuts as

If I put the car in neutral and coast the noise does not go away and the gearbox is changing gear fine.

I did the front diff oil tonight but this made no difference.

Any ideas please?