hi trusted friend...

describe sound disturbance..
go loud as vol. increases?
motor boating?hizzing?cracking?flickering?

(rem. some audio irtermittent /disturbance problem is coz by supply voltage)

is video out good?
try record...then playback to other known good VCR..observe sound...

if good....check output stage...
just to see wethere the problem lies after the audio head...