I have quite a few optical sound prints and the one thing I have found with all of them is they wanted a damn good clean, the thing is though to make sure that once the film is cleaned you get the print completely dry as the optical head seems to pick up on any moisture/cleaner on the film. This is what I have found, the worst being Porridge & Chariots of Fire, great sound but took some work to get there.

I bet you got COF off Ian didn't you Del?