I've gotten crackling noises from my UA-5 from a bad optical mini-plug, too.
On a similar note.... I emailed Doug to see what I needed to do to get a 7-pin cable fixed that would cut out whenever I moved it and he said the 1st thing I should do is check it w/ another patch cable. Lo and behold it was the patch cable. I felt kind of stupid after that one. Happy but stupid. -drew