I've been using X3c since it was released and have never had an issue with noise.  I was recording a bit of guitar yesterday and suddenly I started hearing pop and crackle...almost like an old scratched record only louder.  The strange thing is I was loop recording the guitar and didn't hear the noise the first few times through.  I tried unchecking the 64 bit engine and restarting but that made no difference.  I finally went back and froze all of my synth tracks and the noise stopped.  Very weird that I never had this issue before with even more soft synths.  Also, I've never had this problem with any of the SONAR versions since I got my new system from Purrrfect Audio.  This really does seem to be an X3c issue.  Anyway, I thought I'd post this in case someone else was having the same problem and needed a work around.

It happened to me but only when I used the TH2 guitar plug in. I had to restart and freeze the track.

I'm using Truepianos and Studio Instruments Strings that comes with SONAR...that's it.

Maybe it's the problem I described in this thread?

Also check the "Tailoring DAW buffers" at the end of this post.

I'll check the buffers tonight...thanks for the replies.