Sometimes when starting the transport (either playback or recording) I get what I believe is known as 'motorboating', i.e. there is no sound from the project, just a harsh buzz that persists until I stop and start the transport again. It's maybe 30-40% of the time I start the transport I'll just get a violent buzz.
 
I get this with new projects containing no plugins (just an imported MP3) and with larger projects with many plugins/pro-channel modules. I've tried various settings like enabling/disabling 64 bit precision engine, changing buffer sizes and cache settings. But it still happens.
 
I'm using a Focusrite 2i2 (1st gen) and the latest drivers, and latest CBB
 
Is there any way to diagnose what is causing this and work out how to solve it?

I had a similar problem with the Focusrite 18i20 about a year ago. My solution after a month of this happening randomly was to get rid of the Focusrite. Haven't had the problem since. Sorry if this seems trite, but the unit gave me a lot of grief in the short time I had it. This doesn't mean I think their stuff is bad, just a bad fot for my system and possibly yours.
 
 

I had this with the 2i2 - uninstalling the drivers, rebooting, re-installing & rebooting worked for me.
 
[Edit] - You may have to delete your AUD.ini file too

Also, I don't remember it happening with X3 or Platinum and possibly older Focusrite ASIO drivers.. Focusrite appears to have changed their drivers; the ASIO panel has this crappy Fisher Price interface now..?

The driver I'm using is 4.36.4.484, which is dated June 2017.
 
It looks like the latest is 4.36.5 (Jan 2018).
 
The older driver is working fine for me, and there's nothing in the release notes that indicates I need to upgrade.

emwhy
I had a similar problem with the Focusrite 18i20 about a year ago. My solution after a month of this happening randomly was to get rid of the Focusrite. Haven't had the problem since. Sorry if this seems trite, but the unit gave me a lot of grief in the short time I had it. This doesn't mean I think their stuff is bad, just a bad fot for my system and possibly yours.

 
The 18i20 is a different beast altogether, and only the latest beta drivers have made the USB drivers common to all devices.
 
For the 1st gen 6i6 model and above (so, including the 18i20), everything is integrated into the MixControl app.
 
The Solo, 2i2 and 2i4 don't use MixControl and instead just have the USB driver.
 

Maybe a really short audio loop is enabled?

I saw this on a friend's 2i2, his problem was the latency he was trying to run was way too low for the soft synths he was trying to use.  At first I thought it was a ground loop of some sort, but it really was running too small a latency for the computer and synths he was trying to use.
 

msmcleod
The driver I'm using is 4.36.4.484, which is dated June 2017.
 
It looks like the latest is 4.36.5 (Jan 2018).
 
The older driver is working fine for me, and there's nothing in the release notes that indicates I need to upgrade.

I'd like to try an older driver and see if that helps, but I can't seem to find 4.36.4.484 available anywhere for download.. Focusrite's site just funnels you towards the latest release
 
Any idea where to download older Focusrite drivers?

Alex Bull from Focusrite posted a link on AudioFanzine:
 
https://en.audiofanzine.com/audio-interface/forums/t.10452,scarlett-focusrite-2i4-help.html
 
I'd try msorrels' suggestion of increasing your buffer size first though, before reverting your drivers.