Wheel bearings or something else?

[Cornershop]

Hello folks

Wasn't sure whether to put this in the Suspension or Tranmission section

My recently acquired S8 has always had a rumble audible at speed (40-50 mph plus), which I was hoping would be because of the worn and mismatched tyres all round.

Well, tyres replaced all round today with new Goodyear Asymetric 2, however the 'rumble' is still there and gets louder at speed, irrespective of whether i'm cornering or in a straight line. It quickens with speed, so at 70mph its almost like a washing machine on spin cycle.

Sounds like failed wheel bearings, but as the noise doesn't change with directional changes, i'm less convinced.

What else could cause a similar type of rumble? Quiet at 30mph or so, but gradually gets louder with speed. No vibrations or anything else.

Gearbox was refurbed <10k ago by RA Engineering in Reading, so really hoping its not this! Upshifts appear fine to me, minor stumble when coming to a stop on downshifts. Gearbox drain and refill just completed, but no change on the rumble.

Could it be bearings? low diff oil? driveshafts?

Thanks in advance