Suddenly, I'm getting what sounds like ground noise during my mixdown exports. I've disabled Buss FX, tried muting different tracks, all to no avail. When I'm playing back the mix live in Sonar, no noise issues, when I record in alternate software, no noise whatsoever. Only when I export a final mix, does it show up. I never had this issue before, so  I must have did something to make this issue appear, but what? Here's the link to a sample of the noise
https://soundcloud.com/nullobject001/noise-sample

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

Ok, here's some more input, sorry for not including first time,
Win 7 64 bit
Dell xps 8300 Quad core
8mb Ram
Audio Interface: Roland Quad Capture
Sonar preferences
driver mode: ASIO dithering triangular
Export @24 or 16 bit no change in noise at either export settings
64 bit engine
Sample rate 44100
Last mix, I disabled not only FX bin, but pro channel as well. Same noise. Keep in mind, I have been using the same settings for years, and now the noise has shown up, it's really baffling...

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

Does this happen with every project or just a specific project?
 
Are you using Virtual Instruments in the project?  If so, try disabling them and try a test export.
 
Do you get the noise if you export a single audio track?
 
Which preset are you using in the Export Audio window?  Is it one of the "What you Hear" options or something different?  Either way, try a different preset, preferably one that takes the export directly from the Master track.
 
Make sure the Inputs on all your tracks are set to None in case the sound might be coming from your interface.
 
Kenn
 
 

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?

Glad you found the issue.  You might not need to freeze all your tracks.  Try freezing just the track(s) with an amp sim and see if the problem goes away.  I'd suspect it could be from a particular amp sim component.  Are you using an amp model or pedal you've never used before?  
 
Kenn

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?

nullobject
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?

Doesn't this kind of point the finger at your drums?
What happens if you export just the unfrozen drums with everything else muted?

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.