Default crackly bluetooth

Since upgrading to I9505XXUGNG8 a few days ago I seem to have crackly receive audio on bluetooth, people I call say all sounds good. Multiple bluetooth tried, problem seems to stay with phone. Tried downgrading using O din but it won't let me. Ideas .....
Steve

Samsung S4 on EE 4.2.2 MDM
Xoom US GED 4.0.3

One X on Orange 4.1.1 v3.16.61.6
Sensation 2.3.3 v1.27.161.1
Desire on 2.2
iphone 3gs tried and binned !
Hero - retired