The centre bearing should have a little movement but not a lot.
Quick question, is it just noise or are you getting vibrations as well. If you are getting a vibration, it could be that the two halves of the prop shaft were split and bolted back together out of phase. These shafts are balanced bolted together as a pair and will be out of balance if they are out of phase.
If it is just noise..... does it make noise when idleing??? it could be a thrust bearing.
If it is good at idle and noisy when driving, it could be the bearing at the back of the gearbox.