Hello,
 
After upgrading my notebook and soundcard I'm experiencing a strange problem. Every time I open a project (probably when the audio engine starts) I hear a loud crackle. Then everything works fine: no crackles, no dropouts, no problems shown in latencymon/dpclat. But this crackling "hello" really makes me nervous. Looks more like a software problem, but still not sure (I use NI Komplete 6 audio card). Is there any tweak/workaround for this?
 
Thanks,
Nick.

Try opening devise manager and disable wireless connection. What you might be hearing is interference.

Might the audio interface be re-setting its sample rate when a new project is loaded?

This can sometimes happen even if the projects are the same sample rate, especially if something else (e g Windows sounds) grabs the driver between the projects.

Thanks for your replies!
Wireless is off (the first thing I did), but the sample rate might really be the case. The next question is how to prevent Sonar from doing it. At the moment I see no software that could be sharing driver with Sonar (external soundcard is not used by Windows system audio).

UPDATE: crackling can also appear when I press play in an already opened project with audio engine already running. Again, a short (but loud) click and then everything goes fine, no crackle during playback at all.
 

What mode is your sound card in ASIO or WDM?
Whichever mode, try the other just for fun and science.

Quick Suggestion.  Update your forum signature to include your system details.  (See the signature of some of the other guys in the thread).  This way those responding to your posts know what hardware/software versions that you have.  Click the "User Control Panel" link at the top of the page, to change your signature.

I have close to the same symptoms with my (recently delivered) V-Studio 20. In such case  it also crackles during recording. Setting huge buffer and "most safe" mode in ASIO or big buffer (but not huge, that is worse...) in WDM almost eliminate these effects. That is happening with Win10 on my desktop, with this interface only (I had no such problems with my M-Audio Firewire). On my Win8 notebook (much slower), with default (moderate) buffer settings there is no cracks. Atom based Win10 Tablet, with moderate-big buffers, shows close to the same symptoms as my desktop, but there is Wireless on and I tried to record to SD-card (on which Sonar is also installed... )
 
With all my experience I am a bit puzzled, but I have not invested sufficient time to find the reason (the interface was thought for Notebook in any case, where it is working fine). I have some feeling that Win10 is somehow involved...
 
But for crackling during playback, especially if you start/stop in the middle of audio clips, the reason can be different. In Sonar preferences, Audio, Playback and Recording, try set "Fade on Start" and "Fade on Stop" to 20-50msec.

I use ASIO, switching to WDM seems to improve the situation (haven't tried long enough to say "solved"), but my Komplete Audio 6 doesn't support multichannel output which is essential for me with this laptop setup.

Please determine what "crackle" means. Dropouts can cause "crackles," but they are certainly not the only source of sounds that may be called "crackles." Some people even describe some episodes of clipping as "crackles."
 
It is not uncommon to find hardware causing dropouts and certainly initial "pops" when starting playback. The sudden voltage change on a speaker actuator can cause problems as the tension on the cone abruptly changes. What does the sample-zoomed waveform look like? Does the crackle or pop get recorded in a loopback digital setup? Are crackles recorded on an audio line level connection? Do exported tracks have pops or crackles when played on another wave player? 
 
The usual cures for dropouts will not work if that is not the problem.