Rotated the fronts with rears and noticed quite a difference in tread level. Looking to change the worn rears for 2 new tyres. Been looking online and want to get a pair of Bridgestone Turanza 6 rated  A A and only 71db. Currently all 4 tyres are 285/40/21 and bridgestone alenza but not rated as good, tyres im looking at are 295/40 R21 Y (111). Slightly wider. Wouldnt make a difference would it if i out these on the rears?

Hello Paul,

I guess you are aware that the 285 to 295 difference is the 295 is 10mm wider - seems relatively insignificant on a very wide tyre. 
As with many reviews, tyre reviews can be very subjective, and if noise is your main concern - you mention ‘…only 71db’ - in comparison with ..? - perhaps 72? then I seriously doubt whether you would notice this difference on a like for like pair of same brand tyres.

Again as you probably know, tyres get noisier as they wear and age, so if your concerns are based on current noise levels of your old tyres, you could find this discontent diminishes if you replace with a like for like new set. 
Kind regards,

Gareth.