Hi Mike,
I have exactly this problem detailed here:
Droning/Roaring Noise & Refuelling
and here:
Springs Fitted Upside Down At Rear!!
For info, I still haven't had the 4-wheel alignment done as I don't have £65 spare to gamble with at the mo. I tried switching the rears to the front but this just made the noise & vibration problem worse. Please let me know how you get on with any investigations.