Playing around with some ideas on a mix for a band I'm tracking the other night, I had a strange thing happen.
I had an earlier vocal track that I thought I might be able to use bits and pieces of for doubles. So, I unmuted it, played around with it for a bit, never saved anything, just experimenting.
Now, that track is ALWAYS there! Even when it's muted! I even deleted the track and, it STILL PLAYS BACK!!! I can not get rid of it, can not mute it, can not shut it off!
I've muted it, deleted it, archived it, nothing helps! Anyone else ever experienced this????

Not with audio but with MIDI yes, It was always hidden as a layer under another track. Have no clue how it would get there, This has happened a few time too. 
Can you see all your tracks? 
Click the show layers thingy.. or now is this the dreaded take lanes thingy? 

Cactus Music
Not with audio but with MIDI yes, It was always hidden as a layer under another track. Have no clue how it would get there, This has happened a few time too. 
Can you see all your tracks? 
Click the show layers thingy.. or now is this the dreaded take lanes thingy? 

That's what's happened to me. Usually with a copy-paste function and the focus for the paste was not where I wanted it

I opened the Take Lane thing. Only one track / take in each track.
Opened an earlier Save of the project. All is well there so, I copied the main vocal from it. Opened the problem project, deleted both vocal tracks. Pasted the copied track from the other Saved version. SAME THING!!! It plays back with that other track playing also! Even though it's been completely deleted and replaced.
In all cases, if I Solo the main vocal, it plays fine. No double.
This scares me. I put a lot of time into this version as far as other mixing. Now it's all lost. Gonna have to go back to the earlier version and re-do all that mixing. I'll have to save a new version EVERY time I make ANY change to be sure I don't lose everything if it decides to screw up again! This is just about a deal breaker here! I mean, if you can't trust that the project you're working on is not gonna get corrupted and cause you to lose all the time you put into, what good is it? This might be where I have to go elsewhere.
I don't want to, though. I love Sonar and, I've used it for years but, Man, right now, I've wasted a LOT of time and gonna hve to basically start the mix all over!! Not acceptable! 

if I Solo the main vocal, it plays fine. No double.

 
So presumably if you mute the main vocal you can still hear the "ghost" vocal yes?
 
If this is the case, then you need to work back from you master buss and work out how/where/what signal is driving it.
 
I'd bet at this point you have a hidden track playing
 
Just hit H in console view, make sure EVERY track/buss is selected and click ok.
Start muting tracks one by one until the ghost vocal disappears and you'll have your answer (mute you main vocal first to avoid confusion)

I agree, hidden track alert. This is a powerful function but can completely screw with you if you don't realize it's there. I wish there was an A/B view instead of just a tracklist where you can hide/show.

As soon as I can get back down to the studio, I will methodically try this. I did check this but, it was late and I was kind of in panic mode so, I'll check it again. Thanks!

Wellllll, that's what it was! I had what I THOUGHT was a blank track hidden. Turns out it was my original scratch vocal track, that somehow, got mislabeled. "Unhid" it and Boom! There it was! So glad it was something so simple 'cause, I love Sonar and am glad it was not a Sonar issue! THANKS guys for the help!
 
PS
How do I mark this thread "Solved"? 

edit the subject in the original post

I had that problem once. I laid down a harmony vocal track and forgot turn off my monitors. I was singing along to the main vocal with my cans on thinking that the only thing going into the mic was my harmony. Didn't realise that the main vocal was also being recorded as spill.
So, then when I'd mute the main vocal, to hear what the accompaniment was sounding like, the lead vocal was still there., WTF.
Took me some time to figure out what was happening. What a recruit trick.