I had the same drone noise from the rear of the car but it never got any worse around corners or after a 2000 mile drive.
So not bearings but after reading the forums I jacked the rear of the car up just so the tyre was off the ground, looked at the light passing under the tyre and spun the wheel.
There was a big flat spot on both rear tyres, probably 3-4 mm.
I've got the 19" wheels on my 159 and I guess the previous owner left the car stood for some time causing these flat spots.
Luck the tyres are up for replacement so I've ordered a pair, i'm 100% sure this will cure.
I will ensure I check the tyre pressures monthly and make sure the car is not stood around for more than a week.
You must look after these low profile tyres, I have a sports mercedes with these type of tyres and taken up cycling to work over the christmas period with the car sat on the drive for a few months, when I take the car for it's service they told me both rear tyres had splits on the inside walls.
They were only 6 months only with about 2000 miles put on them.
And no it does not matter if you buy Michelin or Golden Sun tyres they can all do that, don't take any notice of those that say otherwise because the same thing happened to a friend of mine who had new Michelin tyres.
You need to maintain tyre pressure and make sure you car is not sitting around.