I've built this using schematics from AMZ site, but I made my own PCB to avoid wiring and have a possibility to use SMD chip. It works, but there is some kind of noise that is more audible at tone decay. Everything seems fine, connections are OK, solder joints too.
What I am not sure about this build is grounding - shall analog / digital ground be connected together, or not? I have connected them together.
This is my PCB:
(http://i67.tinypic.com/axybew.jpg)
(http://i65.tinypic.com/nbsxza.jpg)
(http://i63.tinypic.com/rh92k4.jpg)
Can you describe this noise a little more? As the note fades?
There is of course a noise gate in the Q&D. That might be complicating your problem.