I discovered something very strange that has me baffled...after listening to a final mix, I wanted to go back and make 1 subtle tweak (muting guitar strum for 1 measure in middle of song)...all of my tracks were frozen, then bounced to one final mix, then archived so I could work on final mix sweetening without CPU loss.  My steps to go back were:
 
1) archive final mix
2) unarchive other tracks
3) unfreeze guitar track
4) mute already mentioned measure
5) bounce tracks again for final mix #2
 
When I compared mix #2 to mix #1, I could VISUALLY tell it wasn't as "fat" (amplitude, I guess)...which was also confirmed when I ran it through my mastering software...by almost 1db in places.  You may notice that I didn't REFREEZE my guitar track.  Sure enough, I did steps 1-4 again...then froze the track...then bounced and it was just like mix #1 again.
 
What would cause the levels to be different whether or not I bounced frozen/regular tracks?  I thought that 2+2 = 4, the same way that 1+1+1+1 = 4...but not in audio rendering perhaps?  Fun!

Minute changes in phase between tracks can change individual peak levels pretty significantly as two peaks align more closely than they did in a previous mix. A change of 1dB in peak level is not a lot and would not be surprise me. But RMS level should not change significantly. Also some plugins have deliberate randomness or unsynced modulation that cause them to produce a slightly different output every time.

There's any number of possibilities. I can think of a couple:
 
* Non-deterministic effects that use some form of randomization to produce a slightly difference sound each time.
* "Double-bouncing". Because unlike any other DAW, "frozen" in Sonar means "Rendered with a bypassed FX bin, it is possible to unbypass a frozen effects bin and then save the project and forget that you've done this. You will now hear the same effect chain applied to a track twice: once on the rendered audio, and once again in the now live FX bin. When you unfreeze that track, the you are back to applying the effect only once, and this changes the color of the sound.

Gain nob?

gswitz
Gain nob?

Negatory...  ;)
 
Thanks for all the posts people...I didn't realize how a bounce/un-bounce/re-bounce could produce such random results/levels...

yevster
...unlike any other DAW, "frozen" in Sonar means "Rendered with a bypassed FX bin...

Just for reference, this behavior is optional in SONAR on a per-project basis. Freezing with FX applied and the bin bypassed is the default for projects started from the Normal template, but can be changed via Freeze Options in the the context menu for the freeze button.

There are so many things it can be and as some stated, very minor tweaks can make big changes.
Also, your freeze properties need to be looked at as you can have it set so your frozen tracks are being played twice through your effects bin. 
 
Sonar will export is spot on, as long as you tell it to do so. If its not, then look at your gain stages and signal chain for your answers
 
CJ

You know, sometimes the scroll wheel has caught me out. I've spun the scroll wheel and modified a volume or a compressor setting by accident. This has happened more in X2 and X3 than before. The new focus paradigm gets me confused sometimes.