Tried using vocal sync this morning, after selecting region and guide, and selecting play, I was exposed to > 100dB blast of high pitched noise, with main fader almost off, I couldn't stop without shutting off my audio interface. Which also happened when I somewhat dumbly tried it again.
Anyone know what's up with that? (sorry, I couldn't hear you, could you repeat that, lol)

Does the waveform look highly distorted, i.e., hitting max level for extended periods of time? We need to narrow down what's producing the noise. Also this is a long shot, but try increasing latency temporarily.
 
Finally, did you call up the region whlie SONAR was playing? I noticed that SONAR doesn't like to do DSP while playing in some cases, for example, normalizing a lengthy section of audio without the transport being stopped.

Grab this free utility and slap it at the end of the signal chain on every project/template you create.
 
http://www.cerberusaudio.com/Software/Products/Ice9/

Have you installed the Update 1 quickfix for Kingston? There was a problem with the 64-bit Double Precision Engine that was causing issues like that. Even if you have the update already, you might try disabling DPE in preferences.

I also experienced this during my first attempt to use Vocal Sync.  Haven't revisited Vocal Sync since.
 
See:  http://forum.cakewalk.com/Big-Noise-When-Using-VocalSync-m3294020.aspx#3311606
 

After going against my nature, and reading vocal sync manual sections, I may not have been using or able to use as intended, also noticed the noise filter selection. I was thinking to synchronize more precisely somewhat different vocal sections, being some harmonized, do-wah, do-wah, do-wah's, with some guide,  lah, Lah, LAh, LAH's,
So I guess there's some restrictions there being, there not basically the same vocal lyric parts, there's some silence between both the do-wahs, and he lah's, 
I guess if need be Id have to do this manually, moving with snap off, or possible using audio snap in someway, or accept them as recorded.
So maybe this could be a warning to others, to read the manual first, or risk exposure to excessively loud screeching sound levels, LOL.
 
    

JohnEgan
... or risk exposure to excessively loud screeching sound levels, LOL.

Well, again, there's no reason ever to have to risk your hearing in this way.  Do yourself a huge favor and grab the free Ice 9 Automute utility from Cerberus Audio (Link provided earlier).  

Same thing happened to me. I posted here about it. Noel was kind enough to check my file, and couldn't reproduce it.
 
For now, I don't think much about using Vocal Sync.

Ok thanks all, and Ill try that ICE9 utility, had I been listening through my 15" monitors I may have blown my brains out. lol
 
Cheers

this is ... actually... kinda funny...