Do you maybe have some mono/stereo/pan law thing going on?
I export tracks to be pitch corrected out to a standalone version of Melodyne so don't use Melodyne within Sonar, but I do recall things being louder when imported back into Sonar from Melodyne.
From what I recall it was something to do with exporting a mono (say vocal) track out but not setting the export option to 'mono'. The track would come back in 3db louder than when it went out. I can't quite remember offhand the ins and outs of it all, but it was something to do with mono/stereo.