Hello -
I noticed today for the first time (well recently) this sudden buzzing noise happening when I press the transport button to play. Obviously in panic you press stop and then when you play again it doesn't happen. This has happened 3 times in the last 20 minutes. The only thing I've changed recently is I now have a scarlett 2i2 instead of the audiophile soundcard. This has happened before but I decided it had happened when the battery in my acoustic guitar was low - when i changed the battery it stopped. Anyway, today it just happened during playback - no recording at all. Anyone know what this event is ?
Thanks
Echo

The 2i2 is buss powered. Try a USB cable with ferrite choke. 

A background buzz or only buzz and nothing else?
 
What sometimes happens to me is Sonar gets stuck in a tiny loop, possibly the audio buffer looping.
If I stop and start again it usually plays normally.