Reset the audio engine before starting playback and see if the problem still happens. There is a button to do this on the control bar.

Thanks gswitz that's how I deal with it. If I toggle the audio engine off/on it will be ok.

In that case, do you think it was a cached sound from before you hit stop? Maybe from a synth or specific vst?

> Thanks gswitz that's how I deal with it. If I toggle the audio engine off/on it will be ok.
 
Try going to preferences -> Playback and Recording and disabling (or enabling) Always stream Audio through FX. If it makes no difference put it back. Also please make sure Share drivers with other programs is unticked.
 
Otherwise the issue is probably the audio drivers (even though you may have the latest, you could try rolling back), or something hanging around your audio buffer for some other reason. Just hunches.

If you happen to get a chance, please listen to this sound and let me know if you have any idea what may be causing it.  I am posting this to emphasize the fact that this is not a typical 60 cycle hum.  It's really a harsh buzz that seems to only occur when starting the transport.  In addition, sometimes Sonar will just stop responding for a minute or two.  After this huge pause, sometimes you hear the buzz.  Sometimes it recovers from the buzz.  Other times the audio engine just drops out.
 
[link=https://skydrive.live.com/redir?resid=FF49D1C9A24E716F%219760]https://skydrive.live.com...F49D1C9A24E716F%219760[/link]
 
Thanks.
 
Ed

Have you updated to X3D yet? If not please do this. Afterwards please RESET and then RESCAN your plugins.
Cheers...

Which soft synths are in your project?

That's for the replies guys.  We are running X3d and have reset and rescanned the VSTs.  The project has quite a few instances of plugins (over 100).  They are all either the plugins provided by Cakewalk or some of our Waves plugins (granted some of them are 32 bit).  The project does not contain any soft synths.
 
We've talked to Cakewalk tech support 3 times and the offered the normal suggestion of updating the Lynx drivers and firmware (which we had already done).
 
Any other ideas would certainly be appreciated.  I think the occasional long delay (measured in 10s of seconds) on when starting the transport is really odd.  Almost like some sort of timeout / reset.  Then, once if get past that initial hurdle, I can restart the transport and if starts right up.  The CPU isn't really taxed.  Even when playing all the tracks with all the effects, it's well under 50%.
 
Thanks, again, for your help.
 
Ed

I do not own any Waves plug-ins, but have seen some posts in passing on Waves and X3, so it may be worth searching the forums on that specifically (try googling "site: forum.cakewalk.com Waves plug-ins X3").
 
The other thing that sticks out is 32-bit plug-ins in 64-bit X3. Some seem to work, and others do not play so well. Threads are out on that topic as well.
 
For where you are, it may be "easiest" to save your project as a new one, and remove Waves/32-bit plug-ins and see if you can get that new project to playback correctly (or create a new project and moving tracks into it).
 
I may have missed in the thread... have you checked the ASIO and I/O buffers on another project?

If you turn off all the plug ins (I think E does this) do you have the issue?
 
Otherwise, it sounds like a buffering issue since you say it takes 10 secs or so for playback to start.