Background hiss with Radio (?)

Volumio Information

Volumio Version:2.834
Hardware: Pi zero
DAC: PhatBeat

Afternoon - I have set up Volumio (running in a a Bush DAC90) - it works but there is a background hiss on radio stations?

Any ideas would be great, its like listening to FM with a slightly weak signal,

edit update - at low volumes there is a constraint hiss when playing, none when not playing. Over volume 55 its not as noticeable but when listening at low volume there is a notable background hiss…