I'm using mac os x 10.6 shooting in hd 10-50i, codec avc intra 100-50i stp gets the file when i send it from fcp for noise reduction. It doesn't return it, altered!! any suggestions yes fcp has stp as audio set up

How exactly are you doing the roundtrip?

highlight audio, right click, send to stp, I.d NOISE in STP, , process, set noise print, then noise reduction, apply, file save return to fcp... diddly squat! no green line on fcp audio, to show any changes. I tried converting audio to an aif file by exporting it to desktop as aif, then importing it into fcp and then overwriting original audio same process as above, this stp does round trip, with green line on audio after, only one problem, IT'S OUT OF SINC!

From the Sequence window, are you sending it to an STP Audio File Project or Multitrack Project? If you send to an Audio File project, the original audio in the Sequence should have (sent) added to the name, and you should see a new file in the Browser "[original name] (sent).aif" or .mov if it's a video clip. If you send to a Multitrack project, you have to save out an AIFF file and re-import that into FCP.