I don't think I've changed anything recently but suddenly I'm getting crackling all over my songs.  Typically a song has up to 20 tracks with soft synths and a modest amount of effects.  The crackling is even present on the intro with just one track playing but does seem to get worse with more tracks.  I've got 8 load meters and they're well under 50% except the first one which is well over.  My laptop and interface should have plenty of power, so I'm lost.
 
So far I've tried disabling the wireless network adapter but it hasn't improved things.  Also did an export and the exported song was fine.  Please help!

Audio buffers too low?
Have you tried bypassing all fx to see if it's a plugin causing the problem?

When I had this it was buffers. It actually increased roundtrip when I fixed the issue FWIW.

Best start is to run latencymon with the project open/running. Latencymon will add its own latency (possibly make playback worse), but will also track what else is running on your machine. Trying to troubleshoot something system specific will be a crap shoot otherwise.

Thanks Wizard.  I checked the Mixing Latency under Preferences/Driver Settings and the buffer size slider was set to Fast (4.4Msec) but it was greyed out so I couldn't see how to move the slider.  I went into the ASIO panel and changed the buffer size from 6 to 8 and things have improved, the slider is still on Fast but now it says 8.7Msec.  Shouldn't I be able to move the slider though?  Any idea why I can't?

That slider is only for WDM, IIRC. grays out when using ASIO but still changes when the ASIO setting change

Hi Guys,
I think we've got to the bottom of it now, thanks for all your advice.
I have changed the buffer size as reported above, I've also downloaded and run LatencyMon which said I should disable WLAN and change the power settings to prevent power throttling.  So I tried disabling the wireless network adapter and changed the power setting to High Performance and then ran LatencyMon again.  This time it said everything was suitable for processing audio, so I am much encouraged.
Once I've posted this I'm going to try Sonar again with the new setup and if everything is OK I'll put this one to solved.
Thanks again!
 

Thinking back, I believe I must've reduced the buffer size to reduce latency when I was comparing Piano VSTs.  Forgot to put it back obviously and I can't remember how I reduced it either!