And its not a bomb

Any idea,s i have checked for stones in the tyre, but it is that sort of sound. however the sound is coming from the offside rear wheel and is a lot more noticeable when taking a long sweeping curve to the left, and does ,nt seem to make the noise when steering to the right, any ideas peeps?
Cheers
Onkers

1.9 DG WasserBoxer 1987 Tintop.