posed this a month ago but got no replys - could this be the centre support bearing? if so any tips?

"Last few weeks have a strange noise which is slowly worsening. It is noticable when de-accelarating from speeds of at least 50mph. It is a faint but noticable whirring/humming noise. No idea if it is present all the time as if it were the engine sounds would mask it unless the accelerator pedel was not pressed. I have an automatic gearbox and if I place it onto neutral whilst slowing at these speeds it makes no difference on the noise. I wondered if it was the wheel bearings but I have jacked up each wheel and there is no play when wiggilling them. Axels seem in good condition with no visible problems. Front brake disks begining to get near limit but warning light not on yet. Any ideas? - car has done 110,000 miles (2004 reg)"