Noise from X3 from mixdown tracks

This is a shot in the dark, but it might have something to do with your Export Audio settings.  Give us some details on the Export settings you're using, along with some specs for your PC and audio interface.  You didn't really give us much to work with to help you.  The sound might be from a bit-rate or sample-rate conversion, or perhaps from something in the ProChannel, if you only disabled the FX Bin, for instance.
 
More info would help us help you better.
 
Kenn

You might try a different dithering algorithm.  There are several to choose from.  Just a shot in the dark.

Well, a breakthrough, kind of...After hours of enabling/disabling FX, pro channel, tracks, sends, etc, I've found out where the noise is coming from at least. I should start by describing my workflow that UNTIL LATELY has worked flawlessly for me. My primary instrument is guitar and I record direct with no FX and monitor amp sounds through my mixer even though they're not printed to the track, that way, I can go back and decide which amp sim sounds best for that particular track. I also use MIDI drums and bass each through it's appropriate sampler, i.e. Triolgy, BFD or whatever. With this workflow I am free to change things on the fly if I want to try something different. I like to keep things unprinted so I can tweak as I go. Here's where the noise is SUDDENLY coming from. In a last ditch effort, I tried freezing all the tracks before export and as you have probably guessed, no noise. So the noise is being added by Sonar as it processes the samplers when they are live during export. The thing that puzzles me is why now? It never did this before. I haven't changed any settings and never had an issue. So now I have to add a whole bunch of freezing of tracks before each export now if I want a clean track. I wonder if there's any way to make Sonar behave like it used to because this adds a lot of extra work each time I want to export a mix. And it still doesn't answer the question of where is the noise coming from?

Nope tried that Kenn. Muted everything except the drums, but kept them live. Noise. Froze the drums. No noise. Same with bass. It has nothing to do with the guitar or the amp sim, that was my first guess, but I was wrong. Three questions still remain, 1. Why did this start all of a sudden? 2. What's causing it? 3. Can I fix it?

No, not at all, not just the drums, it doesn't matter what the instrument is, drums, guitar, bass, anything, the results are the same, live tracks during export = noise, frozen tracks during export = no noise.

Yep, that was about number 4 in the sequence of elimination steps. No difference.

sounds a little like a bad ground.
 
are you using anything when mixing down that you don't use during other operations ?
a light maybe ? a outboard effects rack ?
 
sounds almost florescent.
 
I find in these cases, sometimes, not always.. its the obvious, its something right in front of us that we wouldn't have even thought about.
check your surroundings.

stevec
Very good point Beeps...  The issue was using the Console Emulator with the 64bit double precision option enabled.  However, it's possible to keep the 64bit option disabled during playback but still have it checked on just for export (that's what I do).
 

Are you still experiencing a problem with this, Steve? I thought that was long gone by now.
 
I never experienced it though (and did test it with "b", "c" and I think even "a" for the brief period I had it installed). The only PC noise weirdness I'm getting is from pressing the power button on the Concrete Limiter but I'm starting to think that has something to do with an instance of the Tape Emulator downstream... but I may try disabling 64bit just to see what that does.